Heat

A rash of unexplained fires has the town on edge, and Inspector Jean Darblay's officers have to decide whether they are looking at accidents or at somebody's hobby. Heat is an investigation about connection, the patient business of linking scattered blazes into a pattern that nobody wanted to see.

The work here is not forensics at a single scene. It is the slow assembly of a timeline out of debris and witness accounts, the sifting of coincidence until something more calculated shows its face. Inspector Foster, played by Terrence Hardiman a decade before he took on The Demon Headmaster, brings the fire service's expertise, while Janet Worsley, Ruth and Robert Elliot and a man who answers to Frost, or Charles Reginald Habgood if you prefer the paperwork, all contribute pieces of the puzzle. Darblay runs the inquiry with Sergeant Joseph Beck and Sergeant George Parrish at her side, PC Peter Sims on the ground and Detective Chief Inspector Jim Logan watching the bigger picture.

John Foster wrote it, Paul Ciappessoni directed. Stephanie Turner is Jean Darblay, with David Ellison as Beck, Noel Collins as Parrish, David Gillies as PC Peter Sims and Tony Caunter as Logan. Elizabeth Proud plays Janet Worsley, Lally Percy is Ruth Elliot, Dick Harris is Robert Elliot and Geoffrey Banks is Frost, a man of two names and, the episode suggests, two purposes. It opened the third series on 11 September 1982, and the show trusted its audience to stay interested in a mystery that unfolded one small blaze at a time.

The mystery earns its tension the honest way, through the unsettling feeling that the fires are not random. Professional detachment battles the creeping suspicion that something sinister is underneath the everyday, and the show keeps the two in balance until the end.

It is a measured, patient hour. Persistent questioning, the episode argues, will eventually pull the truth out of the ashes. Sometimes it just takes a lot of questions.