“We’ve been delighted by how well the first series of Counter-Measures was received,” says Big Finish producer David Richardson, “and it’s been an absolute joy to revisit these characters now that the format is established. I really do feel that series two raises the bar.”

Episode one is Manhunt by Matt Fitton, in which Group Captain Gilmore is on the run and suspected of murder. The guest cast includes Lucy Fleming (Mrs Simon Williams, and star of 70s hit drama Survivors) as Lady Waverly, Blake Ritson (DaVinci’s Demons, Upstairs Downstairs) as Captain Astor and Gemma Whelan (Game of Thrones) as Emma Waverly.

The team heads underground for episode two, The Fifth Citadel by James Goss, investigating a hidden wartime bunker beneath London. Celia Imrie (The Best Exotic Marigold Hotel, Calendar Girls) plays Dr Elizabeth Bradley, whose long-standing friendship with Sir Toby might not be enough to save the country from disaster…

The third episode, Peshka by Mark Wright and Cavan Scott, takes Counter-Measures to Holland for an international chess championship, where the contest takes on a deadly significance.

The series ends with Sins of the Fathers by John Dorney, which follows the consequences of a tragic death at a funeral… one that will have major repercussions for Counter-Measures. Tom Price (Torchwood) plays Father Ellard, while Philip Pope (The Hitch-Hikers Guide to the Galaxy) is Templeton, Sir Toby’s trusty assistant.

The five-disc box set includes an hour-long behind the scenes documentary, with interviews with cast and crew.