After his regeneration, the Doctor (Tom Baker) becomes delirious and collapses in front of Sarah Jane Smith (Elizabeth Sladen) and the Brigadier (Nicholas Courtney). The UNIT Doctor, Harry Sullivan (Ian Marter), takes care of him. The Doctor awakes, sneaks out in his night-clothes, and tries to escape in the TARDIS, but the Brigadier and Sarah stop him. They convince him to help find the thieves who stole top secret plans of a disintegrator gun. The Brigadier takes him to the Ministry of Defense Research Centre, where he observes Holmesian clues—a crushed flower and a rectangular footprint. Whoever stole the plans bypassed UNIT traps by burrowing underground to gain access to the gun’s components.
Sarah investigates the National Institute for Advanced Scientific Research, where she finds Director Hilda Winters (Patricia Maynard) and Arnold Jellicoe (Alec Linstead) are creating a robot—Experimental Prototype Robot K-1. It was originally developed by Professor J.P. Kettlewell (Edward Burnham) who thought it had been dismantled. He believes it is unstable. Sarah feels sympathy for the seven-foot-tall hulking brute (Michael Kligariff), despite its menacing look. Later, it tries to kill Professor Kettlewell.
Winters and Jellicoe have told K-1 to kill Cabinet Minister Joseph Chambers as an enemy of humanity and to use the disintegrator gun to open his safe and steal his papers. UNIT finds his body and the Brigadier reveals that the stolen papers were launch-codes of various nuclear powers placed in the safekeeping of the U.K. It turns out that Winters and Jellicoe are members of the Scientific Reform Society, who want to put scientists in control of the world. Sarah sneaks into a meeting and UNIT plans an attack. At the meeting, Sarah learns that the apparently harmless Kettlewell is the mastermind. K-1 discovers Sarah, and Winters orders it to kill her. When UNIT arrives their quarry has fled, taking Sarah as a hostage. Harry sees them enter a bunker and warns UNIT.
Winters sends a list of demands to world governments. Kettlewell is getting cold feet. Sarah and Harry escape. Winter sends K-1 to stop them, but the robot, conflicted and confused, accidentally kills Kettlewell, his creator, and apparentyapparently shuts down. The Doctor stops the countdown to destruction, UNIT takes the baddies away, but K-1 reactivates and attacks UNIT. K-1 searches for Sarah to protect her. UNIT fires the disintegrator at it, but the robot absorbs the energy and starts to grow to enormous size. He picks up Sarah like a doll and places her safely on the roof. The Doctor knows why this is happening and races to Kettlewell’s lab to synthesize his metal-biodegradable virus. This causes K-1 to shrink to nothingness. Sarah is sad because of K-1, but the Doctor offers to take her in the TARDIS, along with Harry.
Ian Marter was hired to play Harry Sullivan in case the Doctor chosen was elderly, like William Hartnell, and they needed someone young for derring-do. Tom Baker was an out-of-work actor working in construction and just about to give up on acting, though he had been in several films. Producer Barry Letts saw him in Ray Harryhausen’s Golden Voyage of Sinbad, which had just hit the theatres. At first, some viewers thought him strange and loony, but he would play the Doctor for seven seasons, twice as long as anybody else. Clearly, I was not the only one to be charmed by his spontaneous Cheshire Cat smile, part impish, part twinkling, and a little bit mad. Writer Terrance Dicks summed him up: if you said it’s a nice day, he would say, “Is it? Is it? By God, you’re right; it’s a wonderful day!” Dicks said the Robot story was inspired by King Kong, which is obvious, but a little Frankenstein was tossed in. The K-1 robot costume was impressive, but the special effects let down the story toward the end, though they were improvedfixed for the Blu-ray release.