In many ways this episode is the culmination of the Chang plot (he’ll return next time, but only for an epilogue). Fittingly, the climax is on the stage of the Palace Theatre, where we first saw Chang, and where in front of a live audience, his showdown with the Doctor plays out in a brilliantly tense sequence where the “safe” peril of the magic show suddenly becomes real suspense as we’ve seen Chang load his revolver and pick out the Doctor as his mark. Of course, Chang gets thrown to the wolves by Greel who, unforgivably, ruins the performance exactly like in The Phantom of the Opera.

Pursuing Chang down into the vaults of the theatre, we finally learn the truth: Chang was a humble peasant, elevated by Greel, posing as the god Weng-Chiang after ‘he appeared in a blazing cabinet of fire.’ But the Doctor’s interference has caused Greel to accelerate his plans and led him to the location of the cabinet. Now, he’s cleared out and left Chang to be the fall guy.

It’s an elegant clarification of the story so far, and the stakes. ‘He could be anywhere. We’ll have to look for him,’ Leela declares. Meanwhile, across London, Greel and Mr Sin have finally got the time cabinet in their hands, and race off into the night, laughing maniacally. This is a superb, game-changing cliffhanger, refocusing the story onto Greel’s ‘dangerous experiment in time travel’.

Next episode: The Talons of Weng-Chiang – Part Five