The one where Steven goes into a strop and storms off the TARDIS...
Steven Taylor thinks his friend the Doctor is dead. He is a space pilot from the far future lost in the folds of history, in a strange time and country where it seems everybody wants you dead because of what you believe in. The only thing I reckon Steven Taylor truly believes in is himself. He is a very self-assured, self-confident character, which probably explains how he accepts the death of the Doctor so quickly and turns his attentions to self-preservation. He and Anne search Preslin's shop looking for the Doctor's clothes, and with them, Steven hopes, the TARDIS key. Because as a self-assured space pilot from the far future, he seems sure he'll be able to fly the TARDIS and escape 16th century France on his own.
I used to think Steven Taylor was a cookie-cutter replacement for Ian Chesterton's Dan Dare heroism, simply a younger incarnation of the requisite masculinity and brawn that formed a key part of Sixties Doctor Who (Ian, Steven, Ben, Jamie). But as I've watched and listened to his episodes through I've come to realise that Steven Taylor was actually quite a selfish, mildly unlikeable man whose stubborn confidence in his own thoughts and opinions never allowed him to become as endearing as his predecessor or successors. Peter Purves performs the written character well, but also gives Steven a certain cocky demeanour which I find slightly irritating.