Sweet Flower of Uthe was a short story in the 1981 Doctor Who annual. It featured the Fourth Doctor, Romana II and K9 Mark II. It dealt with the common science fictional theme of computers having too much power over people.
The Fourth Doctor, Romana II and K9 Mark II land on what the Doctor initially believes is Uthe 4 but K9 quickly corrects is Uthe 3. They find a world with lush vegetation but no apparent intelligent life. Much to Romana's surprise, the Doctor sends K9 off on a mission to find a Uthanian scatterbud, a rare flower that grows only on this planet. They continue on and stumble across a literal hole in the ground.
Before long they are beset by Uthians in military garb, who initially imprison them with a man named Troy. He fills the Time Lords in on current Uthian affairs. A planetary war has been ongoing for 200 years, and the Uthian battle computer has convinced the whole of the military command that the surface is uninhabitable due to the Rad-Plague contamination. Consequently, the computer has ordered the construction of robot armies to wage a seemingly endless war.
Troy is a part of a small group tired of the war. He's been imprisoned because he tried to get to the surface to somehow find the enemy commanders and sue for peace.
As the Doctor processes this, he and Romana are brought before the Supreme Commander. In the control centre, the two time travellers finally meet the computer. The Doctor engages in a battle of wits with the machine. As he asks it a series of questions designed to prove its fallibility, he gives a surreptitious puff on his dog whistle whilst depressing the computer's external communications button. Thus his tiny whistle's sound is carried up and across the surface of the planet. As the questioning continues, he eventually gets the computer to declare the entirety of the planet's surface uninhabitable. At that moment, K9 arrives at the control centre with a scatterbud in his possession. Since the flower only grows on the surface of Uthe 3, this proves the computer is wrong, and the machine's hold on the Uthian community is severed.
The Doctor and his friends take a leisurely walk back to the TARDIS with Troy. Since the battle computer was mass produced, the Doctor knows there will be other civilisations out there that are equal slaves to their models. He charges Troy with the task of tracking down and decommissioning them.
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