Poison

The fifth series closes with "Poison", the darkest hour of its run — a story about a Masonic lodge, a missing fortune and a killer who believes he is God's instrument. The opening is ritual and sudden: at the Faith and Charity Lodge, a financier named Alec Price, being elevated to the Noble Arch, drinks from a shared goblet and dies within minutes. The poison is hemlock, which acts almost immediately and grows naturally on the island. Someone in that room killed him, and the lodge's ancient silences are now protecting a murderer.

John Fletcher's script, directed by Robert Tronson, builds its horror through ceremony. The suspects are the lodge's pillars: Hungerford, who had a financial stake in the hospital the lodge was raising money for; Temperley the lawyer; Patterson the builder, who was to build it; and Dr Michael Anderson, the physician who was to run it. The money — two million pounds raised by a London lodge — has been taken out of the account, and the men who could authorise it are the dead man and the surviving three. Bergerac, who remembers Anderson from childhood, is slow to see the truth: the killer is not after the money at all. When Patterson dies from a mince pie laced with deadly nightshade at the funeral reception, the pattern snaps into focus.

Christian Rodska plays Anderson with a chilling, quiet certainty — a man who has decided the lodge's members are greedy, that the hospital they are building is not for the people of Jersey but for the rich, and that he is the instrument of a God who wants them punished. The climax is the episode's boldest scene: Anderson makes Bergerac pour orange juice into two glasses and choose, then holds him at gunpoint and explains that one glass is poisoned with yew berries, that they have both drunk, and that if Bergerac dies and he survives, it will be proof his actions are right. He dies instead, calmly, certain that God has chosen him.

The coda is cold. The Masons close ranks; Temperley finds the money in an Australian account; and Bergerac, who has spent the episode watching Susan slip away from him — she confesses an affair, a kind of madness, because he is never there — ends it on his knees in shock, the memory of the poisoned doctor ringing in his head. A bleak, precise hour about faith, hypocrisy and the violence of certainty, and a sombre end to a strong fifth year.