Toni turned back to McAlpine. "But you say Michael has a good record."

The lab director looked worried. "He's very conscientious. It's surprising that he should take unauthorized leave."

Toni asked, "Who was with Michael when he last entered the lab?" She knew he must have been accompanied, for there was a two-person rule in BSL4: because of the danger, no one could work there alone.

McAlpine consulted his list. "Dr. Ansari, a biochemist."

"I don't think I know him."

"Her. It's a woman. Monica."

Toni picked up the phone. "What's her number?"

Monica Ansari spoke with an Edinburgh accent and sounded as if she had been fast asleep. "Howard McAlpine called me earlier, you know."

"I'm sorry to trouble you again."

"Has something happened?"

"It's about Michael Ross. We can't track him down. I believe you were in BSL4 with him two weeks ago last Sunday."

"Yes. Just a minute, let me put the light on." There was a pause. "God, is that the time?"

Toni pressed on. "Michael went on holiday the next day."

"He told me he was going to see his mother in Devon."

That rang a bell. Toni recalled the reason she had gone to Michael Ross's house. About six months ago she had mentioned, in a casual conversation in the canteen, how much she liked Rembrandt's pictures of old women, with every crease and wrinkle lovingly detailed. You could tell, she had said, how much Rembrandt must have loved his mother. Michael had lit up with enthusiasm and revealed that he had copies of several Rembrandt etchings, cut out of magazines and auction house catalogues. She went home with him after work to see the pictures, all of old women, tastefully framed and covering one wall of his small living room. She worried that he was going to ask her for a date-she liked him, but not that way-but, to her relief, he genuinely wanted only to show off his collection. He was, she had concluded, a mother's boy.