When the night mail train is robbed by a group of masked gunmen, Pc Joe Mason is first on the scene. Calming a terrified passenger, he moves through the train and is devastated to find the train driver has died from his injuries. Investigating the muddy track and discarded mail bags for clues, Mason is determined to find the violent criminals.

Mason is surprised when DS Rachel Dawson turns up with DI Ludlow, his nemesis from the Met. Ludlow wastes no time in turning the interview room into an incident room and is hostile towards Mason. When it transpires that some of the mail bags contained cash and securities, he orders Miller’s officers off the case. Will Mason do as he’s told?

Next morning, Mason tells Dawson that the robbers might be hiding out in a bolt hole nearby. But Ludlow ridicules this suggestion and announces he has two confirmed leads to follow up. Ludlow seems determined to keep the local police out of the investigation – does he know more than he’s letting on?

Elsewhere, Peggy discovers that a relative of her late husband has passed away, leaving her a legacy.