Secret of the Tower (comic story)

 was the final story in the 1973 Doctor Who Holiday Special. It was unusual for featuring the Brigadier and the Third Doctor in the London Underground, echoing their first meeting in DW: The Web of Fear.

Summary
The Third Doctor and the Brigadier are in the midst of a massive search of the London Underground. They are trying to stop Hingrad, a master of disguise whom the Doctor describes as "the greatest thief in the universe".

UNIT soldiers are on hand to question passengers as needed, when they debark from their trains. One such interviewee reacts badly to being questioned. He runs into the bowels of the Underground. The Doctor gives chase. Under Tower Hill station, he and the Brigadier find that the man has apparently disappeared. But the Doctor notices something wrong with the dimensions of the tunnel walls. Striking a portion of the tiled wall, he discovers a door into a secret chamber.

There, he is swiftly apprehended by Hingrad, who places the Doctor into a stockades that happens to be in what is effectively the basement of the Tower of London. Hingrad aims a cannon at the Doctor and ignites it. The Doctor forces himself out of the cannon's line of fire, while at the same time using the cannonball to rip through the side of the stockades. Now free, he gives chase to Hingrad.

The Doctor is unable to stop Hingrad, even with the help of the Brig's men and some Beefeaters, but his chase after Hingrad has blown the thief's cover. No longer able to sneak around the Tower and make a quiet run at the Crown Jewels, Hingrad is left with only one option: escape via the Thames.

Characters

 * Third Doctor
 * The Brigadier
 * Hingrad
 * UNIT soldiers
 * Beefeaters

Continuity
to be added

Timeline
There's nothing within this story that places it anywhere terribly specific within the Third Doctor's lifetime. The mention of Mike Yates means that it likely, but not necessarily, comes after MA: The Eye of the Giant, which depicts the first meeting of Yates and the Third Doctor. A good, general place for this story, given the absence of any female companions, is likely the gap between DW: Inferno and Terror of the Autons. That said, it's such a quick little story that it really could've happened any time Liz, Jo or Sarah Jane were having a day off.

Those looking for more specific placement might be happy with the completely arbitrary placement between PHS: Smash Hit and (the Third Doctor version of) TVA: The Labyrinth.