Parts: 4
Writer: Christoper H Bidmead
Airdates: 28 February 1981 - 21 March 1981
Production Code: 5V

Doctor: fourth
Companions: Adric, Nyssa, Tegan

Megalomaniac of the Week: the Master

Story: The Doctor has decided it is high time he fixes the TARDIS' chameleon circuit, so he pilots the craft to Earth to get the measurements of a real police box. Unfortunately, instead of materializing the TARDIS around a real police box, he materializes it around another TARDIS...which takes off with the Doctor and Adric inside.

Meanwhile, a feisty Australian air stewardess, Tegan Jovanka, is en route to her first flight with her aunt Vanessa, but their car suffers several flat tires. Tegan goes to a police box to summon aid, but upon entering finds it to be the TARDIS. Half-frightened, half-curious, Tegan goes further into the craft. When her aunt follows her in, she is attacked...and miniaturized.

The TARDIS' cloister bell is signalling imminent danger. The Doctor's greatest nemesis, the Master, has been reborn. And when his plans threaten Logopolis, they also threaten to destroy the entire universe...