William Hartnell
The Chase

Using the new visualiser the Doctor can see events during any time period. Using the device the Doctor notices that the Daleks have their own time machine and are pursuing the TARDIS.

The Doctor tries to escape from the Daleks by materialising in a number of locations in different time periods. The TARDIS is unable to take off immediately from any location as the Doctor has to work out the co-ordinates for the next location, which allows the Daleks to close in.

Eventually, on the planet Mechanus, the Daleks do catch up to the TARDIS. The Daleks attempt to use a robot lookalike of the Doctor to infiltrate the Doctor's compaions. The Doctor and his companions are kidnapped by the Mechanoids, where they are put in a cell with Steven Taylor.

A fierce battle erupts between the Daleks and the Mechanoids causing the mutual annihilation of each. The Doctor then uses the Daleks' time machine to return Ian and Barbara to the twentieth century, two years after they left. Steven, his spacecraft having crashed, joins the Doctor and Vicki in the TARDIS.