The last adventure to star Jon Pertwee. To save the Universe, the Doctor must travel to the planet Metebelis Three, where he discovers an invasion plan of Earth by the Metebelis Spiders, under the leadership of the Great One. To save the planet the Doctor must absorb a lethal dose of radiation, triggering his third regeneration...

Another adventure for everyone's favourite Time Lord. UNIT is called to a sleepy mining town in South Wales to investigate the mysterious death of a miner in an inactive pit. The Wholeweal environmental community believe that a local chemical company has something to do with the death, and when the Doctor heads a mission down the mines he discovers thousands of maggots surrounded by poisonous slime. Further investigation at the chemical works reveals the owner to be under the malign influence of a sentient computer, BOSS.