Time is running out as the Doctor and his companions try to defeat the Daleks before they wipe out all life on Skaro.

Tegana finally makes his move to assassinate the Khan, giving the Doctor and his friends an opportunity to thwart his plans and regain the TARDIS.

The Doctor and his friends must locate the real murderers and the fourth key before heading off for a final confrontation with the Voord

Tlotoxl's machinations result in both Susan and Ian being arrested. With the TARDIS once again trapped inside the tomb, the travellers' only hope for escape lies with Autloc and Cameca.

While the City Administrator's schemes reach their climax, the Doctor and Ian venture into the tunnels under the city to discover the real cause of the Sensorite plague.

Ian finally delivers his message to James Stirling but in order to secure Susan's release he and Barbara are forced into a dangerous spying mission.

The Doctor and his friends face a race against time to expose Forrester's plans and return to normal size before Barbara succumbs to the effects of DN6.