The TARDIS materialises on Earth in the year 1911 inside an old priory owned by Egyptologist Marcus Scarman. Scarman has been possessed by Sutekh, last survivor of the god-like Osirans, who is held prisoner inside a pyramid in Egypt by a signal transmitted from one on Mars. Sutekh desires his freedom and instructs Scarman to construct servicer robots - which look like Egyptian mummies - to build a missile with which to destroy the Martian pyramid. The Doctor foils this plan by blowing up the missile.
He then falls under Sutekh's control himself and is made to transport Scarman to Mars in the TARDIS. Scarman cuts off the signal but the Doctor, now freed of Sutekh's influence, realises that there will be a short delay before it ceases to have effect, owing to the time taken for it to reach Earth.
He rushes back and uses the time control from the TARDIS to move the end of the space-time tunnel that links the priory to the Egyptian pyramid into the far future. Sutekh, travelling down the tunnel, is unable to reach the end in his lifetime, and dies.

S13E21-26
Two alien seed pods are found buried in the Antarctic permafrost and the Doctor realises that they are from a Krynoid, a form of plant life that infects and transforms all animal life on planets upon which it becomes established.
One of the pods infects a scientist at an Antarctic base but the developing Krynoid is destroyed by a bomb set by two men, Scorby and Keeler, who have made off with the other pod for their boss, eccentric plant collector Harrison Chase.
At his mansion in England Chase arranges for the pod to be opened under controlled conditions while a human host - Sarah - is held nearby. The Doctor rescues Sarah, but Keeler is infected. Keeler's transformation into a Krynoid is accelerated by Chase, who has him fed with raw meat.
The creature escapes and goes on the rampage, rapidly growing to giant proportions. Chase decides to turn the Doctor into compost by feeding him into a pulverising machine. The Time Lord escapes, but Chase falls into the machine and is killed. UNIT have meanwhile been called in, and they arrange for the Krynoid to be bombed before it can spread its pods across the Earth.