Its quid pro quo at the 4077th: two bottles of Scotch for secret surgery, and a tank to scare off snipers for an unauthorized shot of penicillin.

The edge of the known universe, in the year 37,166. The TARDIS lands on the planet Zeta Minor, where a Morestran survey team has suffered a series of horrific killings. What dark secret does the team leader keep - and will the planet permit anyone to leave?