Originally transmitted in 1961, The Avengers was a groundbreaking crime adventure series, following the adventures 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 revitalised 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 and download, The Avengers - The Lost Episodes: Volume 4 brings to life four more classic episodes, adapted by John Dorney and Justin Richards.

1. Kill the King by James Mitchell, adapted by John Dorney

When the King of an unstable Far Eastern country visits the UK to sign an oil treaty, Steed is assigned to his protection and discovers that assassins lurk around every corner.

2. A Change of Bait by Lewis Davidson, adapted by John Dorney

Carol's landlord has got into a lot of trouble with a shipment of bananas and a crooked businessman. Fortunately Steed and Keel are hot on the heels of insurance fraudsters and might just be able to save him...

3. Hunt the Man Down by Richard Harris, adapted by Justin Richards

When Frank Preston is released from prison the race is on to find his hidden loot. Can Steed and Keel survive warring gangsters to return the stolen property and rescue a kidnapped Carol?

4. Dead of Winter by Eric Paice, adapted by John Dorney

When the frozen body of a Neo-Nazi is discovered at the docks, Steed and Keel get involved with a fascist organisation developing an apocalyptic plan.

The Avengers - The Lost Episodes: Volume 4 is available to buy and download today.

The three previous volumes are still available, with Volume 5, Volume 6 and Volume 7 available to be pre-ordered now.

The colour years of The Avengers comes to Big Finish with The Avengers: Steed and Mrs Peel, a new range of stories adapted from the classic Sixties comics.

The Comic Strip Adaptations Volume 01 and Volume 02 can be pre-ordered now, as well as a companion graphic novel of the original strips. Special Bundles are also available with free UK postage.