The clatter of the keyboard, a long, drawn-out sigh. ‘Fini.’ Bertrand pushed his chair back and stood. ‘Let’s have a coffee somewhere.’ He grabbed his jacket from a hook by the door. ‘I’d like to escape before some student bumbles in with yet another complaint.’ He hustled Gessen into the hall. ‘I don’t remember being so spoiled at that age. We just got on with things, didn’t we?’ He flung his arm around Gessen’s shoulders. ‘All fired up, weren’t we? With our fierce desire to burn down the world and create a new one from the ashes.’

Out on the pavement, Bertrand hesitated. ‘Shall we go to our usual place, for old time’s sake? It’s been tarted up a bit, but the coffee’s still good.’

Bertrand strode across the boulevard, talking over his shoulder as Gessen tried to match his loping stride. He couldn’t help but smile. Here they were again. Tall, lanky Bertrand striding ahead, with Gessen trotting behind, like a younger brother trying to keep up.

At this time of day, just after four, the cafe was quiet. The marble-topped tables looked improbably the same, and the waiters still wore waistcoats and imperious expressions. But the rack of newspapers was gone, and the once plain walls were stencilled in a design of silvery-blue filigree. A group of students clustered around a table in the back corner, intent on their conversation. Two women, probably tourists, judging by the shopping bags at their feet, occupied the table by the window.

When their coffee was set in front of them, with a pleasing click of porcelain against stone, Gessen breathed in the steam before stirring sugar in his cup. After a minute or two of exchanging pleasantries and asking about each other’s lives, he brought up the reason he’d come to the city.

‘I’ve been working with a new patient,’ he said. ‘Quite an unusual case. Though I’m having trouble getting him to cooperate in his own treatment.’

Bertrand studied Gessen over the rim of his coffee cup, eyebrows raised, but said nothing. Gessen could practically hear the comforting whir of his friend’s thoughts.

‘It appears to be a case of either severely repressed trauma, or even a split identity. Though such cases are exceedingly rare.’ He knocked back his coffee. ‘And it’s not an easy disorder to make sense of, under any circumstances.’ After a pause, Gessen continued. ‘He seems to have suffered a temporary psychosis and attacked a stranger unprovoked. I’ve been working with him for nearly a month, and even though the man is in serious trouble, he’s resisted our every attempt to help him.’

Bertrand ran his hand through his thatch of hair. ‘Do you remember your Socrates? “Sometimes you put walls up, not to keep people out, but to see who cares enough to break them down.”’