'Planet of Evil' (4 Parts) Story Code '4H' by Louis Marks

Answering a distress signal, the Doctor takes the TARDIS the planet Zeta Minor, a planet far out on the edges of the universe. He and Sarah discover that an invisible killer has attacked a geological expedition from the planet Morestra, killing all the members except Professor Sorenson. When a military expedition arrives to investigate, its commander, Salamar, accuses the Doctor and Sarah of the murders and seizes the TARDIS, but the two time travellers are soon proved innocent when the creature strikes again. The Doctor follows the creature back to a pit, where Professor Sorenson has been collecting samples of rocks and minerals. He discovers that he pit is an interface between this universe and a universe of anti-matter, and the creature is retaliating against the removal of the samples of anti matter taken by the professor. The Doctor makes a bargain to return the samples in exchange for the Morestrans to leave unharmed, but Sorenson has smuggled away some samples, and once it has left, the ship is slowly dragged back to the planet due to the anti matter on board. Sorenson becomes infected by the anti matter, and is transformed into an anti-matter monster that drains the life from others. Salamar attacks Sorenson with a radiation source, but this only causes him to multiply, and soon the creatures overrun the ship. The Doctor captures the original Sorenson, takes him back to the planet in the TARDIS. After the Doctor throws him and the samples into the pit, Sorenson emerges unharmed, and he is returned to the Morestran ship, which is now free to leave the planet.

Tom Baker (Doctor Who), Elisabeth Sladen (Sarah Jane Smith), Frederick Jaeger (Sorenson), Ewen Solon (Vishinsky), Prentis Hancock (Salamar), Graham Weston (De Haan), Louis Mahoney (Ponti), Michael Wisher (Morelli), Terence Brook (Braun), Tony McEwan (Baldwin), Haydn Wood (O'Hara), Melvyn Bedford (Reig)

Produced by Philip Hinchcliffe
Directed by David Maloney

TX:
Part 1 - 27th September, 1975 @ 5.45pm - 6.10pm
Part 2 - 4th October, 1975 @ 5.45pm - 6.10pm
Part 3 - 11th October, 1975 @ 6.05pm - 6.30pm
Part 4 - 18th October, 1975 '@ 5.45pm - 6.10pm

Notes:
*Featuring the Fourth Doctor and Sarah