Unruly police detective DCI Charlie Hicks is deeply suspicious of his new partner DI Elaine Renko. But their first investigation exposes a secret that will connect them for life.

Renko persuades a newspaper to publish the Hard Sun dossier. The government shuts down the story but the detectives investigate a killer for whom the 'Hard Sun hoax' is very real.

A murderer confesses to a priest that he wants to challenge God into revealing Himself by targeting those who help others. Grace makes Hicks an offer.

London is under siege as Blackwood's reign of terror escalates, and Father Dennis becomes a public pariah. Hicks deduces where Renko has hidden the Hard Sun flashdrive.

The murder of a jogger has dire personal implications for Renko but she pretends it is a routine investigation. Hicks makes a startling revelation about the Alex Butler murder.

An internet killer is targeting people who believe they wish to die and Mooney thinks he knows how to trap him. Renko and Hicks change tactic and bring the fight to Grace's door.