She glanced at her phone. She opened and closed WhatsApp, flicked through Instagram, then depressed herself with a few minutes on Twitter. She mostly followed politicians and political journalists, and the rage these days was disheartening. It felt like the place everyone went to shout at each other.

She forced herself to put her phone in her pocket and leave it there, which was always surprisingly hard when she was on her own. The sky over the Tiergarten was a brooding, portentous grey, with only the faintest lick of dawn light. The silence felt oppressive. Once upon a time, trips abroad had been accompanied with the regular buzz of the phone in her pocket relaying messages from Stuart, just the everyday frustrations – and sometimes pleasures – of a man left alone to look after his children. And of love. For the first time since his departure, she was aware of truly missing him: his laugh, his smile, his episodic thoughtfulness and concern for her, not to mention the physical affection and warmth.

She wondered when she would next have sex. Before she died? When she was eighty?

Kate finished her tea and was about to get up when her phone buzzed. It was a WhatsApp message from Sergei. How are you?

She stared at it. Was he telepathic? She messaged back, Am good. Are you in London? Her heart raced with the same kind of force as it had in the days when they had almost become lovers as students in St Petersburg, a world and half a lifetime away.

No, at home in St Petersburg. Be great to see you sometime.

Kate looked at that for a long while. What was he up to? What was it about? She couldn’t think straight. She hadn’t seen him since a meeting at the US ambassador’s party in London at the height of Operation Sigma. And she hadn’t heard from him since she’d travelled to his family’s dacha in the Gulf of Finland, north of St Petersburg, expecting to have everything explained – his role in the GRU, the reason for tipping her off about the meeting of the Russian intelligence elite on Igor’s super-yacht, the identity of the secret mole, Viper, in MI6 – along with confirmation that the prime minister really was working for the Russians.

Instead, she’d found Stuart waiting on the beach, with confirmation that he was Viper, and it was all over.

Except nothing was over. In her more troubled moments, she thought the game the Russians were playing might only just have begun.

She put the phone into her pocket and immediately took it out again. How? she typed. Where?

But there was no reply. She opened the photograph attached to his feed. It was of him smiling against the backdrop of a long beach and the Gulf of Finland, his family’s dacha just visible in the distance. She waited and waited – and then could contain herself no longer. Are you there? she asked.