Strange forces are at work in Amsterdam and two backpackers get caught up in them.
The Doctor is to be confined until a warrant of termination can be issued.
The grief-stricken Nyssa flees back to the TARDIS, where Damon learns that his repairs have been to no avail.
Realising that Tegan is his only hope of locating Omega, the Doctor sends Nyssa back to the TARDIS.
Tegan falls once more under the influence of the Mara and directs the TARDIS to the planet Manussa.
Tegan's disturbing dreams are dominated by the image of huge snake's skull.
With the Doctor imprisoned, the Mara sets the TARDIS co-ordinates for Manussa, his home world.
As the commemorations begin, nothing seemingly stands between the Mara and its spectacular return.
Caught in a warp ellipse, the TARDIS is drawn to a huge spacecraft orbiting Earth.
At Brendon School, the Doctor enlists the help of the Brigadier.
Mawdryn and his eternal mutants are awake and reveal the truth, they are exiles.
The Doctor's ethics are challenged, the two Brigadier's finally meet, Turlough plots with the Black Guardian.
The TARDIS has to make an emergency landing on a ship that is en route to the derelict space station Terminus.
The Doctor and his companions are trapped amongst the victims of the highly contagious Lazar's disease.
The Doctor and his companions have reached the Terminus, discovering a terrible danger.
The Doctor tries to wrest the TARDIS free of the disease-ridden space station
The TARDIS's power is drained away just as the Doctor receives a dire warning from the White Guardian.
The Doctor realises that Striker and his officers are Eternals and that the human crew mean nothing to them.
Captain Wrack manipulates Turlough, because she is also working for the Black Guardian.
The race for the Enlightenment is over and a winner has been crowned. Turlough must make a decision.
At a medieval joust between Frenchman Sir Gilles and Hugh Fitzwilliam, the TARDIS appears.
The Master and the Doctor fight for control over Kamelion's mind while Turlough and Tegan make new allies.