The Doctor's TARDIS lands at the Snowcap space tracking station in Antarctica in December 1986. A routine space mission starts going wrong. When the base personnel's suspicions are roused, the Doctor informs them that the space capsule is being affected by the gravitational pull of another planet — a tenth planet in the Solar system.
The Doctor (1)

Polly

Ben Jackson

The Doctor (2) (uncredited)

General Cutler

Barclay
Dyson
Schultz
Williams

Terry Cutler
American Sergeant

Tito
Wigner

Radar Technician

Geneva Technician
R/T Technician
TV Announcer

Cybermen (voice)

Cybermen (voice)

Cyberman
Cyberman

Cyberman