Synopsis: A fugitive alien is on the run--and in the direct path of the materializing TARDIS. The collision draws both ships into a parallel universe. There, both ships slam into the "real world" BBC Television Centre on 12 October 1979.
The fugitive turns out to be none other than Beep the Meep, who immediately uses black star radiation to take control of the occupants of Television Centre. Beep captures the Doctor with his black star radiation, too--but refuses to believe that it is the Doctor. (Beep's previous encounter with the Doctor was with the Fourth Doctor, and the figure before him is the Eighth.)
Izzy remains free, however, and encounters a man in this strange universe who can help. Inside the Television Centre is an actor filming a show based loosely upon the Doctor's life--and he looks exactly like the Fourth Doctor.
In other words, it's up to Tom Baker to prevent Beep the Meep from using the BBC transmitter to enslave the whole of this universe's Britain with his black star radiation.
Once the all-clear is sounded and Beep has been dispatched to a local zoo, Izzy explains to the Eighth Doctor that she had "special" help defeating the Meep. To help explain precisely what happened, she produces a copy of the first issue of Doctor Who Weekly . . .
Notes: This self-referential storyline unabashedly celebrates the 20th anniversary of Doctor Who Magazine. Interestingly, it ends up wallowing in the culture of BBC House in the late 1970s. If you're British, you'll have fun spotting non-Doctor Who television personalities and properties at play. If you're not, it might not make a whole lot of sense.