In theory the TARDIS should be able to change its appearance to blend in unobtrusively wherever it happens to materialize. In practice, however, because of a fault in the chameleon circuit, it always looks like a police box – a minor inconvenience the Doctor 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 arch-enemy, 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
Christopher H. Bidmead reads his own thrilling novelisation of the last adventure for the Fourth Doctor