“Now, the number seven. This is the reason I mentioned the possibility of a parallel evolution. It is literally a factory, consuming dead blood cells of all kinds and birthing new ones, including its own type.”

The room was silent for some time. Finally, Dr. Weintraub, the cellular biologist, spoke. “Doctor what kind of breakdown process occurs?”

“This blood sample is exceptionally resistant to morbidity. I suspect it would even cause such diseases as virally induced cancer to be self-limiting and transient events in the life of the organism. If this blood was flowing in the veins of a mortal being, subject to time and accident, it might itself be immortal.

“Structural detail of the seventh leukocyte?” Weintraub’s eyes were tightly closed, he was deep in concentration.

“Complex tripartite nuclei. The structure appears to change according to the type of cell being consumed and reproduced. They birth living versions of the other types as fast as the originals die. The blood is in the lab now, six hours old, still as fresh as the moment it was taken.”

“Doctor, surely that’s a side effect of preservation—”

“Doctor Hutchinson, the sample I am referring to is being held at a temperature of fifteen degrees Celsius. It ought to be dead and decaying by now. But in fact we could reintroduce it into the donor’s veins if we wanted to. It’s quite self-maintaining.”

Sarah could hear the rustle of suppressed movements. She looked around the table and was at first perplexed by the uniform woodenness of the faces. Then she understood that they were all holding themselves in, restraining every outward manifestation of their excitement. All except Hutch, who was beginning to look like a little boy attending a carnival. Tom’s power play seemed more and more superfluous. Sarah suspected that Hutch’s type was that most dangerous of opponents for the Tom Havers of the world: a truly committed man—or truly clever—or both.

A face appeared in the doorway behind Dr. Rush. Sarah excused herself; the resident she had detailed to hold Mrs. Blaylock looked upset.

“She left,” he said with a squeak. “I waited a few minutes for her to dress and when I went to the cubicle she was gone.”

Sarah restrained her first impulse, which was to shake him. “Did reception see her go? Try to stop her?”

“She never went through the reception area.”

“Then how did she leave?” He said nothing. Riverside was a labyrinth of nineteenth- and twentieth-century buildings all thrown together, she could have gone in any number of directions. Sarah clutched at a possibility. “Maybe she’s gotten herself lost.”

“Her stuff is gone. She intended to leave.”