One of my favourite Peter Davison sequences ever occurs in this episode. It's when he, Nyssa, and Richard Mace are trapped in the crashed Terileptil spacecraft, being pursued by, as The Doctor calls him, the friendly neighbourhood axeman. Davison's energy when he's bouncing around the capsule, picking locks with arrows, and rushing out the door again is just infectious. After the escape hatch explodes, Davison quick pokes his head up and announces "Let's go!" - brilliant stuff!
I never really noticed before, so early in Davison's reign as The Doctor, at how physical a Doctor he is. Jon Pertwee may still be the king of action, but even then, it was in short bursts. Davison's Doctor always seems to be running, even when he's standing still. It's an exhilarating performance that is such a breath of fresh air after years of scholarly, aged Doctors. I perhaps never noticed how sprightly Davison was until we had David Tennant's performance to compare it to.
Another delightful performance in this story comes from Michael Robbins as Richard Mace, who plays another de facto companion The Doctor, following on from Bigon and Todd (do you think the writers on this new series of Who had the same confidence in the regular companions as JNT had?) . Robbins is helped by some delicious lines written for him by Eric Saward, who probably had more fun writing Mace (something he had done previously in a non-Who setting) than he did anyone else in this story. Saward seems to be channeling his inner Robert Holmes with some of his choices of words and dialogue, proving that, like his penchant for arguments aboard the TARDIS, Saward's admiration for Holmes was also evident in the early stages.