A photoshoot on an army base turns sinister when one of the models is found dead, and the investigation is complicated when Sam Thursday is revealed to be involved. With Thursday side-lined by protocol, Endeavour and Strange take the lead on the investigation for the first time without their mentor. Tensions rise, and the pair clash as their differing opinions push their friendship to breaking point.

After the mysterious disappearance of a teacher, Endeavour finds himself undercover, investigating the dark and secret world of a public school. When a body is unexpectedly discovered, Endeavour has to question who he can trust - and uncover the truth about the crimes before more people are hurt.

Meanwhile, with news that Cowley Station is due to close, Thursday is determined to solve the ongoing unsolved murders linked to Eddie Nero, and charges Fancy with tracking down the elusive Cromwell Ames. But when the investigation ends in disaster, Cowley CID find a surprising link to Endeavour's investigation at the public school. In the shadow of the tragedy, Endeavour and Thursday find some unexpected answers to their cases.