He leaned back and pried two strips of an ancient set of Venetian blinds apart to see the world outside. “The limits on that integral should be minus infinity to plus infinity, not one to infinity,” he said. “It’s a waveform.”

“It wasn’t meant to be,” she said, “when I wrote this stupid equation out. Where have you been?”

“Getting shot at.” He let the blinds ping back. “Being thrown into the back of an ambulance, I think, or how else would I have got to the hospital? Having my internal defib machine poked. Nearly thrown off the top of a church by a two-meter-tall nun.”

“Orly?” She stepped forward, made her black hand blacker by rubbing out the offending symbols and replacing them with the correct ones, using her impossibly neat copperplate.

“Yeah. Really.” He unzipped his jacket and peered at his chest. The ends of black thread sprouted from his skin like a half-buried spider. He had a thought and scooted across the room to his desk. Buried in the bottom of a drawer was a T-shirt, the relic of a death metal concert some six months earlier.

Pif turned around just as Petrovitch had shucked his jacket onto the back of the chair.

“Eww,” she said. “Sam, some warning, Okay?”

He ignored her protests and dragged the black T-shirt on over his head. It was slightly too small; it accentuated his thinness and rode up above his waistband when he raised his arms.

“Have you got anything to eat?” he asked, looking through the rest of his desk, then under the piles of printout and monographs. “I’m not feeling so good.”

“In a minute,” she replied, glancing back over her shoulder at the whiteboard.

“I’ll never do your coding for you again.”

“All right, all right.” She threw up her hands and raided her bag for an energy bar.

When she’d launched it across the room at him, and he’d missed it, she pulled her own chair toward his and sat backward on it, resting her chin on the backrest.

Petrovitch scrabbled on the floor for the foil-wrapped bar, and crawled awkwardly to sitting again. They looked at each other, then she reached forward and took his chin in her fine fingers, turning it left and right. Her fingernails were painted with randomly generated Mandelbrot sets.

“How bad is it?” Her beaded hair jiggled softly as she talked.

“Bad enough,” he said, and finally tore through the wrapping. He continued around mouthfuls of sweet, sticky crumbs. “The defib machine took too long to kick in, and then it wouldn’t stop firing. A lot of heart muscle had gone anoxic, and I won’t get that function back.”

“What are you going to do?”

“I have two options. Get a new heart or die soon.”

She blinked slowly. “You mean cake or death?”

“Pretty much, except the cake I want costs two hundred and fifty kiloeuros, plus expenses.”