Gessen sniffed the air. ‘Anise, I believe, with a dash of nutmeg and cardamom. Don’t you like it? At this time of year, the housekeeper likes to place little sachets of her secret spice blend in all the rooms to put us in the mood for the holidays.’

‘I thought you were Jewish.’

Gessen’s chin tilted up in surprise. They’d never discussed religion before. Like most psychiatrists, he presented himself to his patients as a cipher, a blank slate upon which they could inscribe their own lives. ‘Indeed, I am. A quarter Jewish, on my mother’s side.’ He paused to move his knight to f4. ‘But that’s never stopped me from celebrating Christmas at the clinic. Many of the patients miss sharing the holidays with their families. We keep it fairly secular, so as not to offend those of a different faith. And I’m sure you’re aware that many – if not most – Christmas traditions pre-date Christianity. Evergreens, yule logs, sparkly lights. All pagan traditions meant to lessen the terror of the midwinter darkness.’

Vidor’s gaze was fixed on the board, his expression dull, eyes unfocused. He plucked his queen into the air and moved it to a precarious position. Was he just going through the motions, or did he want to lose? Within two moves, Gessen had placed his bishop next to Vidor’s king. ‘Check.’

This seemed to have an effect. Beads of sweat formed on Vidor’s brow. He frowned and shook his head, as if he’d never seen a chessboard before. He grabbed a pawn clumsily and moved it one square to the left. He sought Gessen’s eyes. ‘Is that a good move?’

Gessen’s heart quickened. Something was happening. ‘It’s an excellent move.’ But Vidor’s king was now wide open to attack. Should Gessen pretend he didn’t see the mistake, or go in for the kill? Better do it now, while Vidor seemed to be under some kind of spell, as if his mind had come untethered from his brain.

With his bishop, he knocked over Vidor’s king. ‘Checkmate. Sheikh mat.’

Vidor’s face paled. His pupils dilated.

‘Sheikh mat,’ Gessen repeated.

The words seemed to arouse Vidor from his stupor. ‘Sheikh, what?’

‘Mat. It’s the Arabic version of the word “checkmate”, a twist on the original Persian, meaning the king is dead.’ When Vidor turned his face towards Gessen, his eyes had changed into those of a frightened child. ‘I’m not dead,’ he cried in a strangled voice. Bewilderment turned to accusation. ‘You tried to kill me, but I’m still alive. Ne me parle pas comme si j’étais stupide.’