Things are getting foggier outside the lighthouse, and inside its getting busier and testier and, in places, funnier. Tom Baker is at the height of his powers, even if he hates the director and is being mean to his co-star, whilst the writer could do this programme brilliantly in his sleep and the director is a veteran sci-fi wrangler. Add to that a pitch perfect guest cast and a superb setting and Martin Geraghty must be spoilt for choice. This is definitely an episode that provokes an impassioned commentary track: strap yourselves in.