Frank Skinner's Perkins was an engaging and loveable guest star. A keen conspiracy theorist, he had already begun studying the mummy before the Doctor turned up on The Orient Express. He certainly proved his worth as the Doctor's willing assistant. He seemed to have some knowledge of the TARDIS mechanics too, so much so that the Doctor asked him to continue travelling with him. So it was quite a surprise when Perkins politely turned down the Doctors offer of more adventures. It is this moment that suggests there is more to this lowly space engineer than meets the eye. Does he know something about the Doctor that made him decide not to take up the offer? Is he really an engineer of a space-travelling train at all? Perhaps the answer is that he isn't quite the nice guy we all thought he was. Perhaps he really is Gus. That would certainly explain the reason the villain never showed his face. If that is the case, we might see something more of Perkins in the weeks to come.