Originally transmitted in 1961, The Avengers was a groundbreaking crime adventure series, following the activities of John Steed, a suave secret agent investigating Britain's strangest crimes - aided by the dashing Dr. David Keel. Together, they pitted themselves against the underworld's most devious and colourful villains.

Sadly, 24 of the 26 episodes of the first series no longer exist; but Big Finish have revisited these missing episodes in a series of audio box sets, starring Anthony Howell as Dr. Keel, Julian Wadham as Steed, and Lucy Briggs-Owen as Carol Wilson.

Now available to buy on CD and download, The Avengers – The Lost Episodes: Volume 5 brings to life four more classic episodes, adapted by John Dorney, Dan Starkey, Rae Leaver and Phil Mulryne.

5.1 Nightmare by Dan Starkey, from a storyline by Terence Feely

When one of his patients, an experimental scientist, goes missing, Dr Keel ends up impersonating him. But not all doctors are on the side of the angels.

5.2 Girl on the Trapeze by Dennis Spooner, adapted by Rae Leaver

The circus has come to town - but after Keel witnesses an apparent suicide, it becomes clear that the clowns are concealing something sinister behind the scenes.

5.3 Crescent Moon by Phil Mulryne, from a storyline by Geoffrey Bellman and John Whitney

On a Caribbean Island, Steed finds himself caught up in a curious case of kidnapping, where if he wants to save a missing girl, he's got to find out what's really going on... and quickly.

5.4 Diamond Cut Diamond by John Dorney, from a storyline by Max Marquis

A smuggling ring is leaving a trail of bodies in its wake. Steed goes undercover as an air steward to investigate, but can he confront the culprit before it's his head on the block?

Starring Anthony Howell, Julian Wadham, Lucy Briggs-Owen, Stephen Critchlow, Harry Long, Bryan Pilkington, Jane Slavin, John Banks, Paul Thornley, Miranda Raison, Chris Porter, Tracy Wiles, Robbie Stevens, Faye Castelow, Anjella Mackintosh, Dan Starkey, Jot Davies, Damien Lynch, Luis Soto, Alice Haig, Helen Goldwyn and Justin Avoth, The Avengers – The Lost Episodes: Volume 5 is available to buy and download today from the Big Finish website.

Four previous volumes of Lost Episodes also be ordered today, with Volume 6 and Volume 7 available to pre-order. And remember, when you choose to buy this release on CD directly from Big Finish, you will also unlock instant access to a digital copy for download.

The Avengers return in May with The Avengers – Steed and Mrs Peel: The Comic Strip Adaptations Volume 1, starring Julian Wadham and Olivia Poulet. You can pre-order the new box-set, alongside Volume 2 and a companion graphic novel of the original strips, all as part of a special bundle.