Paradoxcide by Richard Dinnick is the second story in the Big Finish audio release of Recorded Time and Other Stories.
While fixing the TARDIS, the 6th Doctor picks up a distress call which Peri recognises as being in her own voice. They visit the lost planet of Sendos, a deserted world with a fabled impenetrable arsenal. There, they run into others intent on stealing the super-weapons. When the Doctor can’t break into the arsenal for them, they hijack his TARDIS with a view to going back to a time before the arsenal was created and stealing the weapons before they’re stashed away, only the heavy-handed antics of the weapons-hunters creates a paradox from which they cannot escape.
I generally detest stories that use paradoxes as plot devices when those paradoxes are unresolved. If the chicken-and-egg syndrome is not resolved, then the whole things leaves a bad taste in my mouth. Much of Moffat’s nooWHO does that. Paradoxicide doesn’t entirely escape that, with certain weak conceits required to push the plot along (such as the Doctor suddenly figuring out how to open the arsenal back in the future, making the whole “travel to the past” bit rather moot and leaving it just as an awkward plot device).
There’s very little that will surprise anyone with this story (although nooWHO Moff-fans will probably think the “timey-wimey” stuff is clever), but Colin Baker captures his 80s era Doctor extremely well. You could imagine this being part of his own era. Peri seems to play a pivotal role in the story, but she only does so because the Doctor tells her to (another requirement the writer forces on him to shore-up the paradox).
This time around, the short running time works in its favour because you wouldn’t want to linger on this one for 4 episodes for such a weak pay-off.