Episode 4

Tom Marwood has stopped being a case and become a vendetta. His campaign is aimed not at a target but at Luther himself, and at everyone Luther cares about, with the destruction rained down on everything he touches. The episode opens with the fallout already spreading. Marwood's reach keeps extending, and the show makes his patience scarier than his violence.

Schenk and Gray arrive to move Mary Day to safety, hurrying her to a place no one can find. But the hour immediately raises a question the show is in no hurry to answer: is Mary's protection really Stark's priority, or is she just bait in a game designed to pull Luther into Marwood's trap? And the uncertainty hangs over every scene. The episode is cleverer for refusing to resolve it cleanly. Everyone involved has an angle, and Mary is the piece they are all playing.

Neil Cross wrote it, Farren Blackburn directed. Elliot Cowan's Marwood is a proper villain, the kind who does his damage with paperwork and patience rather than fists, and Idris Elba's Luther responds the way he always does, by going straight at the fire. Sienna Guillory's Mary is caught between her own danger and the larger game, Warren Brown's Ripley and Dermot Crowley's Schenk work the edges, and Ruth Wilson's Alice Morgan shows up to remind everyone that Luther has debts in other directions. Georgina French's Natalie Green and Simon Wilson's Dr Joe Green add to a cast that keeps its plates spinning.

The blurring of protection and entrapment is the point. The episode asks you to watch every friendly face and wonder whose game it is serving.

It ends on a cliff that would be cruel if the show had not earned the right to it. Marwood has made his move, and Luther is exactly where he wanted him.