Logopolis

In theory the TARDIS should be able to change its appearance to blend in unobtrusively wherever it happens to materialise. In practice, however, because of a fault in the chameleon circuit, it always looks like a police box — a minor inconvenience the Doctor now hopes to correct.

Fixing the mechanism involves a visit to Earth and a trip to the planet Logopolis — normally a quiet little place that keeps itself to itself.

But on this occasion the meddling presence of the Doctor's archenemy, the Master, ensures the disruption of normality. And even the Master is horrified by the threat of total chaos he unintentionally precipitates — until he finds a way to turn the imminent destruction of the universe to his own advantage...