The story of Operation Market Garden—a failed attempt by the allies in the latter stages of WWII to end the war quickly by securing three bridges in Holland allowing access over the Rhine into Germany. A combination of poor allied intelligence and the presence of two crack German panzer divisions meant that the final part of this operation (the bridge in Arnhem over the Rhine) was doomed to failure.

On the planet Alzarius in the alternate universe of E-Space, the Doctor, Romana and K9 find survivors of a crashed starliner, strange creatures lurking in the marshes and a genetic riddle which stretches back centuries.

After an encounter with the Master, an airline stewardess named Tegan Jovanka becomes an unwitting stowaway aboard the TARDIS as it travels to the planet Logopolis. There, the Doctor discovers that the Master's interference with the Logopolitans' advanced mathematics has unleashed a wave of entropy which threatens to consume the entire universe.

The Doctor needs somewhere peaceful to recover from his traumatic regeneration. But the sanctuary of Castrovalva is not all it seems, as the Master will stop at nothing to gain his revenge over the Doctor...

The cast and crew discussing the transition from Tom Baker to Peter Davison, including exclusive behind-the-scenes footage of the regeneration.

Hanging by a Thread: The Making of Logopolis is a documentary about the production of the Doctor Who story, Logopolis, which aired in 1981. It is part of the Season 18 Blu-ray collection of Doctor Who. The documentary explores the challenges and complexities faced during the filming of the story, including the transition from Tom Baker to Peter Davison