This episode starts to pay off the growing tension there’s been between Marco and the TARDIS crew. Tegana changes tack slightly from scheming to kill Marco and his followers to sowing the seeds of mistrust in the camp. This feels like a necessary development, because by now Tegana’s previous plots have all failed, and he’s starting to look as incompetent a villain as Wily E. Coyote. Instead of yet another episode where he lurks about having conversations with this week’s minion and cackling, he starts to drip poison in Marco’s ear, exploiting the Doctor’s awkwardness, and twisting Barbara and Susan’s actions to make them seem conniving and untrustworthy. There’s also a shockingly gruesome moment when he swears he’ll finish the ‘magician’ Doctor off with a stake through the heart.

The upshot of all this is that Susan and Ping-Cho are separated, the Doctor’s secret repairs to the TARDIS have to be even more clandestine, and Ian and Barbara, who’ve previously seemed to be enjoying this bit of historical tourism, are now as keen to get away as the Doctor is. Meanwhile, Lucarotti ensures that Marco doesn’t come across as a credulous fool by giving him good justification for not turning on Tegana: to do so would jeopardise the fragile peace. He points out the weakness in Susan and Ping-Cho’s ‘evidence’ against Tegana – which in a kids’ TV drama would probably have been enough to convince him. And, finally, he catches the Doctor with the spare TARDIS key, proving at least part of Tegana’s point.

For an episode that’s focus is on complications, largely to artificially extend this adventure, The Wall of Lies is well structured. Even the title is apt: Tegana’s wall of lies is the barrier between the time travellers and the TARDIS. Plus, obviously, this is the one where they reach the Great Wall of Cathay. This tends to obscure the fact that we’ve hit a kind of holding pattern: Tegana plans a dire fate for Marco; the TARDIS crew foil it, however unwittingly; Marco narrates a bit more of the journey, which is the only indication of any real progress. This could go on for weeks more.

The Wall of Lies no longer exists. Not in any of its regenerations. This review is courtesy of the excellent Loose Cannon reconstruction

Next episode: Rider from Shang-Tu