An alien physician, a scholar invited into the Vatican archive, and an angel who is not told everything — and one question older than all of them: what makes someone a person?

THREE DOCUMENTS DISAGREED ABOUT A KEY.

That question had belonged to a son. Now it belonged to a dying world.

Elyra is an old inhabited world of copper evenings and broad inland seas, and it is dying. The virus does not destroy the body; it corrupts the body’s decisions about repair. Kael, a physician, knows his young patient is getting worse because the child asks about the sea. Searching a restricted archive for anything that might help, he recognises the date before he reads the name: his father’s — the man who left Elyra when Kael was a child and never came back.

Jacob Francis has been invited to the Vatican because three documents disagree about a key. In the Archive he finds two elongated forms crossed near their lower thirds: at first glance keys, at second glance perhaps not, described by a restorer as being “in the manner of keys, though without wards”. Then a medical report from 1941 gives a body temperature no human carries — and in St Peter’s Square a very tall stranger answers, quietly, “That is close to normal for me.”

A novel about evidence and about belief that makes neither one the villain. The cardinal, the archivist and the security officer are each guarding something real; institutions, as one Elyran says, conceal ignorance more often than they conceal knowledge. Seraphel is an angel — not God, not omniscient, sent without being told everything — and he decides for nobody. And someone, decades ago, had already understood that the first danger was not deciding what species the man belonged to. It was deciding whether he was a person.

THE SUBJECT IS NOT TO BE DESCRIBED AS A SPECIMEN.