The Doctor responds to Ace’s request to experience the Summer of Love in 1967 by bringing her to Soviet Russia in 1967, where strangely-helmeted motorcyclists are trying to track down a man who’s stolen classified experimental weaponry. Immediately recognizing the weapon, the Doctor knows that it’s unsafe not just in civilian hands, but in any human hands. At an official reception, the time travelers home in on wildly out-of-place businessman Markus Creevy, who has both personal and professional reasons to be mingling with members of the KGB. He’s employed by the owner of the alien weapons: Ice Lord Hhessh, on a mission to retrieve some of the Ice Warriors’ most sacred relics before humans can defile them with further experimentation. But Hhessh isn’t the only alien on the scene. A Time Lord is operating incognito on Earth, and the Doctor is doing his bidding by letting Ace do most of the work.
written by Marc Platt
directed by Ken Bentley
music by Simon RobinsonCast: Sylvester McCoy (The Doctor), Sophie Aldred (Ace), Ricky Groves (Markus Creevy), Beth Chalmers (Raina Kerenskaya), Nicholas Briggs (Hhessh), John Albasiny (Major Felnikov), Nigel Lambert (Adjudicator / Wolshkin / Glarva), John Banks (Yevgeni / Yasha Lemayev)
Notes: Originally titled Ice Time, Thin Ice was conceived as the opening story for the ultimately unmade fourth season of Sylvester McCoy’s tenure ads the Doctor, though past interviews and articles have indicated that the goriginal story would’ve taken place in ’60s London. The “Time Lords assessing Ace” plotline was originally a major feature of Earth Aid, which would have been the second story of the unmade 1990 season.
Timeline: after Survival
LogBook entry and TheatEar review by Earl Green
Review: One of the longest-delayed stories in Doctor Who history, Thin Ice finally answers – to some extent – what we would’ve seen had the series continued into the 1990s. Unlike quite a few of Big Finish’s seventh Doctor/Ace stories, which tend to take their cues from the New Adventures novels of the ’90s, Thin Ice rolls the clock back to the end of Survival, the point at which the BBC hit the pause button on TV Doctor Who, but continues with the final season’s more assured, maturing style of narrative and dialogue.
But the scripts were never actually written, as the Doctor Who Production Office was shut down before significant pre-production (other than writers’ meetings) could take place in 1990 – this is an adaptation of an idea that was never quite fleshed out into full script form in the first place. Ever since details of the never-made 
27th season were published in the ’90s, it’s been known that this story would have formed part of Ace’s swan song. I normally go out of my way not to spoil stories in my reviews, but in this case it’s necessary in order to critique the story: most of Thin Ice seems to be barreling toward Ace’s departure, which then doesn’t happen. There are two reactions to the change in the story: disappointment that the story has been fundamentally altered (probably with the aim of keeping Raine around for original Big Finish stories in the future), and yet an understanding that not altering the story outline of one of the best-known unmade stories could’ve alienated those who already knew what to expect. In the end, it’s probably best to shake things up and thwart the audience’s expectations/foreknowledge.
The Cold War overtones of the story are almost funny in retrospect; originally the sixties setting would’ve marked this story out as a period piece, but now the pre-Glasnost arms race elements make it a period piece within a period piece. The return of the Ice Warriors would’ve made this comeback as atypical for the creatures as The Curse Of Peladon was in the 1970s. It doesn’t significantly alter the Ice Warriors but, like Peladon, places them in what seems like an unlikely situation. In 1972, we didn’t expect to see Ice Warriors as noble diplomats; audiences in 1990 wouldn’t have expected to see a sympathetic Ice Warrior as the paymaster behind a caper right out of a swingin’ sixties heist movie.
Thin Ice is ultimately very satisfying, despite the controversy that the alterations to the story is sure to stir up. It really does feel like the first story of Doctor Who’s 1990 season.