The plan is that Derren, true to the spirit of his tv specials, kidnaps them all, erases their memories, and arranges for them to wake up a deserted warehouse, wandering around in confusion. It's part of his plot to learn the identity of the Stig (much like the CIA's trying to do in the other, far longer amnesia fic with Some Mongolian Guy who keeps trying to get slash with Richard, which I will post when I've won the crackfic list challenge, or it's done, whichever comes first). Assorted middle bits happen, it all goes wrong, and Derren blows his whistle, resulting in a crowd of backup dancers rushing out and distracting everyone with their spangly costumes and choreography. Derren flees in the confusion, and the Stig has to fix everyone's memory so they can go home.