They walked back up the track to where they had left the car.
Well, that's that,' said Nikolai.
Not quite.'
Grushko drove a short way along the track and then turned off to park behind a line of trees. They could just see the dacha and Dr Sobchak's car parked out front. Grushko wound down the window, opened the glove box and started to sort through his cassettes.
Nikolai regarded him with puzzlement. It seemed an odd time to stop and listen to music.
Keep an eye on the dacha will you?' said Grushko, throwing cassettes over his shoulder and on to the back seat.
You reckon she was lying, sir?'
Those beta emitters you heard me describing? They're alpha emitters.'
Nikolai looked impressed. Where did you learn that?'
From that book I was looking at when we were in there. No, Dr Helen Sobchak was very keen for us to leave, otherwise she would have corrected me, don't you think?'
He found the tape he was searching for and pushed it into the car's cassette-player.
Still, this should tell us for sure.'
It was the KGB recording of Mikhail Milyukin's telephone conversations. Grushko had played it many times and knew the tape virtually by heart. He listened for only a second and then pressed the fast-forward button on the machine until he found the excerpt that he was interested in now:
I've got a little job for you, if you're interested.'
What sort of material are we talking about?'
Dr Sobchak's voice was unmistakable. Grushko smiled with some satisfaction.
I knew I'd heard that voice before,' he said, and, winding the tape back a little, he played this small section of dialogue again.
Mikhail Milyukin spoke to Dr Sobchak three days before he was murdered,' he said, reminding himself.
Why don't we just go back in there and confront her with it?' said Nikolai.
Grushko shook his head. It might yet come to that. First let's see if there was a reason she wanted to be rid of us.' He stuck his face in the way of the sun and closed his eyes. Besides, it's a lovely day for a spot of surveillance.'
Fifteen minutes passed and Grushko sighed contentedly. No harm in waiting a little while longer, he thought. The name of the game was patience. Then an engine started and Nikolai tapped him on the leg.
So much for her guests,' he said.
They ducked down as the white Zhiguli came laboriously up the track and past the line of trees that screened them.
Grushko started his own car and, after a decent interval, followed her. At the top of the track she stopped and then turned on to the main road, heading east in the direction of the city.
Grushko was an old hand at traffic surveillance. He knew that on a country road you could hang well back and allow four or five cars in between. Dr Sobchak was not a very quick driver and he could afford to give her some space. But he was suspicious when quite soon afterwards she turned off the main road and drove into Petrodvorets.
Maybe she's going to drive around and see if she's being followed,' he said.
Maybe she's going sightseeing,' Nikolai suggested.
Petrodvorets was certainly worth a look, with its lovely palaces, extensive gardens and numerous fountains. But Grushko was not impressed by this idea.
No, we spooked her back there at the dacha and no mistake,' he said. She's not out for the drive. She's going somewhere specific, I'll bet my pension on it.'
They followed the white Zhiguli along Krasny Prospekt until it pulled up by the railway station and Dr Sobchak got out. For a moment Grushko thought she was going to board a train for the city but then she crossed the road and went in the entrance to the main park.
The two detectives left their car and, in an effort to blend in with the tourists, they removed their jackets and rolled up their sleeves before following. By this stage Grushko was intrigued.
What's she up to?' he said as they meandered through the trees, trying to look inconspicuous.
Maybe you're right, sir,' said Nikolai. Maybe she is trying to cover her tracks.'
Is that what they teach people in radio-biology?' mused Grushko. Perhaps we should have stuck a radioactive tracer on her ourselves.'
As they came round the front of the Great Palace of Peter the Great and walked along the sea canal that split the park from north to south they were suddenly aware that Dr Sobchak's leisurely pace had become something more urgent.
She can't have seen us,' grumbled Nikolai as they broke into a gentle trot.
It was then that they saw the hydrofoil.
Dr Sobchak mounted the gangway and the very next minute the white craft started to draw away from the landing point. Grushko swore loudly.
Of course,' he said. It's only thirty minutes from here to the city centre. I should have realised. Why waste petrol when she can go in and out for a couple of roubles?'
They turned and started to run back towards the station. It was several minutes before they reached the car again. As Grushko started the Zhiguli's small engine Nikolai was looking at his watch.
Can we do it?' he puffed. It had been an effort keeping up with the smaller, lighter man.
Just about,' said Grushko. But even if we don't, I think I know where she's going.'
They watched the hydrofoil dock at the pier in front of the Hermitage from a safe distance. It was mostly foreign tourists getting off, their pockets stuffed with dollars and black-market roubles, but even among so many people Dr Sobchak was easy to spot in her comparatively shabby clothes. It always amused Grushko how even Russian-speaking foreigners could imagine they might escape identification. Once he had confounded an Englishman, a fluent Russian-speaking friend of Tanya's who had bought all his clothes in Russian stores, by identifying him within only a few seconds and without one word exchanged. Grushko had explained to the man that what had given him away was the smile on his face: there was, he said, little for any Russian to smile about as he walked along the street.
Dr Sobchak stepped off the hydrofoil and turned north up Dvorkovaya towards the Lenin Museum. But she wasn't smiling.
What now?' said Nikolai as they observed her walking away in the opposite direction.
Grushko found first gear and slipped the clutch. As they drove past Dr Sobchak Nikolai knew better than to look back.
My guess is that she's going to take a tram across the bridge,' said Grushko. A Number 2, I should think.'
He stopped the car on Suvorov Square and lit a cigarette.
Are you going to tell me?' said Nikolai.
Well, can't you guess? The First Medical Pavlov University. That's where she's going.'
As Grushko had predicted she caught a Number 2 bound for Petrogradsky Region. The Kirov was the longest bridge in the city, with four lanes of traffic north and south, and the tram ran along on a track in the central reservation. They followed it across the bridge and then along Kubyseva Street.
It must be nice to be right all the time,' grumbled Nikolai.
The tram terminated on Kapayeva Street right in front of the modern red-brick building that was the University Hospital. Dr Sobchak got off and walked across the front lawn and into the entrance.
Grushko and Nikolai got out of the car and walked up to the hospital. They showed their identity cards to the security guard who met them inside the door.
The lady who just came in,' said Grushko. Dr Sobchak.'
The security guard nodded.
Where did she go?'
Up to her laboratory. That's on the second floor and along the corridor to your right as you come up the stairs. Room 236.'
