Subterraneans (1)

A millionaire businessman vanishes. A year later he turns up dead, and the state of him says he spent that missing year as somebody's prisoner. Not a ransom job, or not only one: the question this half keeps circling is why anyone would hold a rich man captive instead of simply selling him back.

The case widens from there, as these cases do. Two decomposed bodies come into the picture, one a suicide and one very much a murder victim, and the thread tying them together is a single medical researcher. Boyd's team starts pulling at that connection, and what emerges is the sort of quiet horror the show does best: respectable professional lives with something rotten running underneath them. The title is doing more work than geography.

It's a strong opening hour. The forensic puzzle gives Felix Gibson plenty to chew on while Grace Foley reads the psychology of a man who was caged for a year by people who never explained themselves, and the episode trusts both to carry real weight rather than decorating around the plot. There's also a fine unease in watching wealth prove useless against whoever held him. Money buys privacy, and privacy is exactly what got him taken.

Barbara Machin and Ed Whitmore wrote it, Michael Offer directed, first shown in October 2005. Trevor Eve leads as Det Supt Peter Boyd, with Sue Johnston as Dr Grace Foley, Wil Johnson as DI Spencer Jordan, Esther Hall as Dr Felix Gibson and Félicité Du Jeu as DC Stella Goodman. Toby Stephens plays Dr Nick Henderson, with Nicola Stephenson as Julia Henderson, Ayesha Dharker as Mary Sharman, Ronan Vibert as Dr Jonathan Lynch and Kelly Harrison as Tina.

What lingers is the captivity itself. A year in someone's power leaves marks that forensics can catalogue but not explain, and the show knows it. Part two has some explaining to do.