'I said you had gone when I came back from the toilet at the Cafe Engel. There was no time for her to ask me any questions. She and Matalainen had to leave right away.'

'Christ.' Eusden had to look away for a moment. Confirmation that Pernille must have concluded he had run out on her was even harder to bear than he had expected.

Timo leant across the table and poured their coffees. There was silence for a minute or two as they each contemplated the awfulness of what had occurred that day. Then Osmo said, 'When the police spoke to me, they had no idea what caused the explosion or even how many people were killed. There's a man in hospital who they think might be involved, but he has a serious brain injury. They're not sure he's going to survive. There's also a man they're looking for who they think was in the street when the explosion happened. The neighbours said he left in a hurry.'

'Me,' said Eusden dolefully.

'If I was you, I think I would fly home to England and pretend you were never here.'

'I can't do that.'

'But what can you do if you stay?'

'Make Tolmar Aksden pay for what he's done.'

'You'll fail,' said Timo, sipping his coffee.

'Maybe. But that's better than not trying. That's better than... living with his heel on your neck.'

The two brothers exchanged an eloquent glance. Timo cleared his throat. 'What do you want to know?'

'Tolmar Aksden's secret.'

'We don't know it,' said Osmo. 'No one does.'

'Not quite no one,' Timo corrected him. 'Arto Falenius knows, I'm sure.'

'Falenius? Head of Saukko Bank?'

'Yes. Grandson of the founder, Paavo Falenius.'

'Timo used to work for Saukko,' said Osmo.

'You did?'

'Forty-two years, Mr Eusden. Eighteen to sixty. Paavo Falenius was still alive when I started there in 1949. It's a long time ago. Some of the senior staff had been there from the beginning.'

'And when was the beginning?'

'1899. But it was just called the Falenius Bank then. The name Saukko wasn't used until the nineteen twenties. In English, saukko is an otter.'

'Why the change?'

'Paavo never explained. He had a reputation for not explaining things. But it wasn't the only change. The bank expanded greatly at that time. It was quite a small business until about 1920. Then, suddenly, it was big, rivalling Union Bank, Finland's oldest joint-stock bank. That took capital. A lot of capital. And no one really knows where Paavo got it from. But everyone who worked for him benefited from how profitably he used it, so...'

'Is that the secret? Paavo Falenius's money?' Eusden remembered the cache of pre-war Finnish currency at Nydahl's apartment in Copenhagen. 'Ever heard of Hakon Nydahl?'

'Yes.' Timo looked surprised. 'I have. He was one of our customers. A very special customer.'

'In what way?'

'His account was managed personally by the chairman, Eino, Paavo's son, Arto's father. Everything relating to it had to be referred to Eino. The only other customer who ever got treated like that...was Tolmar Aksden.'

'So, they're all tied together in some way. Hakon Nydahl, Tolmar Aksden and the Faleniuses.'

'Yes.'

'And what is the connection?'

'Like Osmo said, we don't know. But...'

'But what?'

Osmo interrupted in Finnish before Timo could reply. There was a flurry of exchanges between the two brothers. Though Eusden could not understand a word, he had the impression that an argument they had had several times before was being repeated. Eventually, it petered out. And Osmo made a gesture with his hands that looked like a concession of kinds.

'There is a man I know, Mr Eusden,' Timo said, slowly and carefully. 'His name is Pekka Tallgren. Twenty years ago he was a history lecturer at Helsinki University. He planned a book on revolutionaries active in Finland before the First World War. Lenin, obviously, but there were many others, mostly Russian. Tallgren came to us to Saukko for information about Paavo's links with these people. Paavo had been dead many years by then, of course. Tallgren said he had evidence that Paavo had provided several revolutionary groups with funds. He asked if we had records of these dealings. We referred his request to the chairman. Arto had only recently taken over the chairmanship from his father. He was... embarrassed, it seemed to me. He told us Tallgren was to be given no information of any kind. Tallgren soon realized he was getting nowhere. He stopped asking his questions.'

'What happened to his book?'

'It was never published. Several years later, after I retired, I met Tallgren in Observatory Park. He was not in a good state. He told me his publisher cancelled his book contract soon after he approached us. Then one of his female students complained he had molested her. He denied it, of course. He was suspended. He started to drink heavily. He never went back to the university. In the end, even though the student later withdrew her complaint, he was dismissed.'

'Arto Falenius arranged all that?'

'Or Eino did. He was still a powerful man even after he handed the chairmanship over to Arto. Tallgren told me it was when he asked Arto about one revolutionary in particular that his troubles began.'

'Who was that?'

'I can't remember the name. But Tallgren will remember for sure.'

'You know how I can contact him?'

'I felt sorry for him, Mr Eusden. So, I gave him a little money and helped him find somewhere decent to live. He sobered up, I'm glad to say. Later, I...recommended him for a job. Do you know Suomenlinna?'

'No. What is it?'

'A small group of islands out in the harbour. The Swedes constructed a fortress called Sveaborg on them in the mid-eighteenth century to defend their eastern frontier against the Russians. Later, the Russians took it over. And, later again, we Finns. It's a tourist attraction now. It includes a museum where you can learn about the history of the fortress. That's where I helped Tallgren get his job. He works as a curator in the Suomenlinna Museum. And he lives out there, in an apartment block on one of the islands. I think... if I asked him... he would speak to you. Yes, I think he would.'

'Then, ask him.'

'You're sure you want me to?'

Eusden nodded. 'I've never been more sure of anything in my life.'

FORTY-FOUR.

It was gone midnight when Eusden reached the Market Square pontoon, but a couple more ferry crossings to Suomenlinna were still to be made. The cold had become more intense than he had ever experienced. The sea ice moaned and creaked. His breaths were plumes of frost in the still, deeply sub-zero air.

The few passengers, Suomenlinna residents bound for home, huddled in the cabin as the ferry chugged out through the broken skin of ice on its channel across the harbour. Eusden sat staring at their reflections in the windows, including his own gaunt, drained and hollow-eyed. He spun Lund's phone in slow circles on the table, wondering if he should call Gemma and tell her... But since he did not know what he should or could tell her, he made no call.

He scrolled idly through Lund's contacts list. Tolmar Aksden was there; so, too, was Arto Falenius. He was tempted to call one of them or both. He wanted them to know, even though he was well aware it was better they did not, that he was coming after them. They had overreached themselves. This time, he willed them to understand, there would be a reckoning.

The tower above the main gate of the fortress loomed through the chill mist that hung over Suomenlinna as Eusden stepped ashore. A single figure was waiting on the quay, wrapped in a parka with a huge Arctic-standard hood. 'Richard Eusden?' he enquired, pulling off a mitt to offer his hand. 'I'm Pekka Tallgren.' They shook. 'Cold night for a boat trip, no?'

'Thanks for agreeing to talk to me, Mr Tallgren.'

'Call me Pekka, Richard. OK?'

'OK.'

'I bet you're thinking: why does the crazy man live out here on this frozen island?'

'Timo said you work here.'

'I do. But sometimes... it feels a bit like Alcatraz, with San Francisco across the bay. Anyway, let's not stand here, freezing our balls off. I brought the car with me.' Tallgren turned and led the way towards a tiny old Fiat. 'It's not far to my place. But everywhere's a long way on a night like this.'

'Sorry it's so late.'

'Don't worry. I don't sleep so good.' They clambered into the car. Tallgren threw back his hood, revealing a bearded, heavy-featured face. He started the engine and skidded away along a sparsely gritted strip through the surrounding blanket of snow and ice. 'I've got interested in astronomy since I came here. You can see so much more this far from the lights of the city. Not when it's like this, of course. You're not keeping me from my telescope, that's for sure.'

They rumbled over a narrow bridge to an adjoining island and turned left past a high stone wall. 'How long have you lived here, Pekka?' Eusden asked.

'Nine years. Some exile, hey? But, truthfully, I like it. I'm near Helsinki but not in it. That suits me. It keeps my memories at just the right distance. Timo told you all about my... troubles, no?'

'Yes. He did.'

'He helped me a lot. More than he needed to. So, I owe him. Which is lucky for you. I don't normally talk to anyone about Saukko.'

'I know. I'm grateful.'

'Maybe you shouldn't be. Knowing this stuff... can be unhealthy.'

They crossed a second bridge to a further island and slewed to a halt in a courtyard flanked by barrack blocks converted into apartments. Most of the windows were in darkness and a profound silence closed about them as they climbed from the car.

'Welcome to my world, Richard,' said Tallgren.

The apartment was small and felt smaller still thanks to the crammed bookshelves lining every spare wall and the piles of books and papers that had overflowed on to the floors beside them.

Stripped of his mitts and parka, Tallgren looked just what the domestic disorder might have led Eusden to expect: untidily dressed, grey hair overdue for a trim a middle-aged academic content in his own shambolic environment. Except that he was an academic no longer.

'I set some coffee going before I left,' Tallgren said as Eusden hung up his coat in the tiny hallway. 'You want some?'

'Fine.' Eusden would have preferred a stiff drink, but he knew better than to ask for one.

'Come into the kitchen. It's the warmest room.'

An aroma of coffee had filled the kitchen in Tallgren's absence. An electric percolator stood ready on the crumb-strewn worktop. He grabbed a couple of mugs and waved Eusden to the table opposite, where a crumpled copy of Helsingin Sanomat lay, folded open at the page in the business section Eusden had seen earlier, with the photograph of Tolmar Aksden and Arto Falenius. Tallgren pushed it aside as he delivered their coffees.

'Black OK? I'm out of milk.'

'No problem.'

'And cream.' Tallgren nodded down at the newspaper. 'Looks like they got it all.'

'Do you regret tangling with them?'

'You bet.' Tallgren took a reflective sip of coffee, then sat down and folded the paper back on itself. The faces of Aksden and Falenius obligingly vanished. He smiled. 'I've seen enough of that pair.'

'What can you-'

'Hold on.' Tallgren raised his hand. 'This is how it's going to work, Richard. You give me the full story of what brought you here. The whole thing. Then, if I'm convinced you're not... some kind of spy for those bastards... I'll tell you everything I know. You're sitting here with me because of Timo. No other reason. I don't know you. He says I can trust you. OK. But that's a two-way street. And you've got to trust me first. Do we have a deal?'

It was a relief in many ways to have no choice but to share everything he knew with somebody else. Tallgren sipped his coffee and smoked his way through a couple of roll-ups while Eusden recounted the events that had brought him to Suomenlinna. He took out the double-headed-eagle envelope and showed Tallgren the piece of paper with the fingerprints on it. He talked about Marty and Clem and all the people he had met in the course of one desperate week. He held nothing back. He laid it all on the line.

When he had finished, Tallgren topped up their coffees and said, simply, 'It's worse than I thought.'

FORTY-FIVE.

'I'll assume you know as much Finnish history as the average non-Finn, Richard, which is zero,' said Tallgren. 'So, I'll try to keep it simple. Sweden surrendered Finland to Russia in 1809, but Tsar Alexander the First granted the Finns self-government. He knew he'd have too much trouble with us otherwise. The Grand Duchy of Finland, as it was called, was part of the Russian Empire, but not part of Russia. It ran its own affairs. That made it a haven for anti-Tsarist revolutionaries Bolsheviks, Mensheviks, anarchists, nihilists in the years before the First World War. It became Lenin's second home. He and Stalin met for the first time at a Bolshevik conference in Tampere in 1905.

'I set out to write a full study of the revolutionaries active in Finland during that period. It was a fascinating subject. I never thought it was dangerous as well. The Falenius Bank, as Saukko was called back then, was mentioned in a lot of correspondence as a source of loans to such people. Well, Arto Falenius was willing to admit his grandfather lent money to revolutionaries, though he denied they were gifts in effect, never repaid. He also denied Paavo sheltered mutineers who took part in a short-lived Red uprising here on Suomenlinna in 1906. It was odd. The evidence was clear and I couldn't see a problem. Paavo Falenius was a socialist sympathizer. Good publicity, I'd have thought.

'Then I came across some other information that confused the picture. Lots of new stuff was leaking out of the Soviet Union around then thanks to glasnost. It turned out from some of it that Lenin suspected Paavo Falenius was a double agent, feeding information about the revolutionary groups to the Tsarist government in St Petersburg. True? I never found out for sure, because that was when I really got Arto's attention, by probing his grandfather's relationship with a shadowy character called Karl Vanting.

'Vanting was Danish, born in Copenhagen in 1884. He moved to Helsinki in 1905 specially to offer his services to Lenin as an active revolutionary. He played a big part in organizing the 1906 mutiny and a general strike the same year. The story was that he was a bitter enemy of the Romanovs because he was an illegitimate son of Tsar Alexander the Third. It could be true. There was supposed to be a resemblance. And my researches showed his mother worked as a maid in the Danish royal palace of Fredensborg. She was dismissed in December 1883. Karl was born five months later. Pregnancy was probably the reason for her dismissal. The Tsar and the Tsarina, Dagmar, went to Fredensborg with their children every summer to visit their Danish relatives. So, the timing fits. Karl's mother married a Copenhagen shopkeeper called Vanting in 1885 and the boy took his stepfather's name.

'The same material that quoted Lenin as suspecting Paavo Falenius of working for the other side mentioned Vanting as his alleged confederate. This is where it gets murky. Vanting left Helsinki in 1909, destination unknown. It took a lot of work to follow his tracks. He dropped out of revolutionary politics altogether and turned up on the Caribbean island of St Thomas, working as a clerk for the aide-de-camp to the Governor of the Danish Virgin Islands. The aide-de-camp's name was Hakon Nydahl. Denmark sold their Virgin Islands colony to the United States in 1917 and Nydahl went home. Vanting didn't go with him. He stayed on, working for the new American administration. Then, in the spring of 1918, he got himself attached to a US regiment sent to intervene in the Russian Civil War. He spoke quite good Russian and they were short of interpreters.

'The Russian Civil War was the Whites against the Reds crudely speaking, Tsarists versus Bolsheviks in the aftermath of the Revolution, complicated by parts of the old Empire trying to break away and British, French, German and American forces trying to grab territory and/or stop the Reds winning. Plus rescue the Tsar if they could. Finland declared independence from Russia at the end of 1917 and then had its own Reds against Whites Civil War. Unlike in Russia, the Whites won, with a little help from the Germans. It was all over by May 1918. Thousands had died. And thousands of Reds had been taken prisoner. This is where they were held. Here on Suomenlinna. The fortress became a prison.

'What's this got to do with Karl Vanting? Well, one day in October 1918, two people arrived in Suomenlinna in a small boat they said they'd rowed across the Gulf of Finland from Russia. One of them was Vanting. The other was a lad in his early teens. Vanting didn't say anything about serving in the American army and he claimed he didn't know what had been happening in Finland. Unfortunately for him, the prison commandant remembered him as a Red revolutionary. He and the lad whose name wasn't recorded were locked up.

'Conditions here in 1918 were terrible. Overcrowding. Disease. Famine. Vanting couldn't have chosen a worse place to land. But he wasn't here for long. After a few weeks, he and his companion were released on the recognizance of Paavo Falenius. And then... they dropped out of sight.

'It gets even murkier now. Like Timo told you, the big unanswered question about Saukko Bank is where their influx of capital in the early nineteen twenties came from. Well, what you've found out fills in the gaps in a theory I thought was really off-the-wall when I first developed it, but now... fits together like Lego. A Danish invention, no? Lege godt. To play well. And they did play it well.

'Paavo Falenius was a double agent. Not much doubt about it. Maybe the best kind. The kind both sides trust so completely you have to ask: which side was he really on? He was born in 1869. Studied law at St Petersburg University. One of his fellow students was Peter Lvovich Bark, who also went into banking and was the Russian Minister of Finance from 1914 until the Revolution. He fled to England afterwards, where he became Sir Peter Bark, a director of the Bank of England. Strange, no? But consider. Bark acted as executor for the Tsar's estate after his presumed death. Only he knew how much money there was and where it was. Falenius was an old friend of his. I found photographs of them together in a university rowing team and later at banking dinners in Helsinki and St Petersburg.