There's a secret locked up in UNIT's Vault 75-73/Whitehall. Dr Elizabeth Shaw is the only one left who knows what that secret is.

Returning to UNIT for the first time in decades, she slowly unravels the past. The vault contains the remains of a spaceship that crashed in the Pennines in the Seventies.

For the young Liz Shaw, the priority is to ensure the thing's safe. But the Doctor is more concerned about the alien pilot. And the chance this ship offers for escape. Can he resist the temptation, or will the Doctor turn on his friends?

Written by Simon Guerrier, Doctor Who – The Companion Chronicles: Shadow of the Past presents a gripping new mystery for Liz Shaw, performed by the wonderful Caroline John, with Lex Shrapnel as Marshall. You can download your copy today for just £2.99 from the Big Finish website. Listen to the trailer below:

Liz returns with the Third Doctor this month to take on the Meddling Monk. Doctor Who – Short Trips: The Blame Game is performed by Rufus Hound and can be pre-ordered today for just £2.99; with a money-saving subscription to a whole year's worth of Short Trips also available.

You can explore Big Finish's full range of Doctor Who Companion Chronicles on the range page here: including the recently release Doctor Who – The Companion Chronicles: The Second Doctor Volume 1.