I do love this story, but it's a bit all over the shop. Clearly the elephant in the room is the filming cock-up which cut down the final scene so considerably. The denouement itself is a total mess.

There are other problems too. The sets are of perfectly decent quality, but there's no real distinction between the bits in Hungary and the bits in...Mexico is it? Peru? We never really get the sense it's actually set in either. Nor do we understand how the scientists are underground in one and able to activate volcanoes in the other. The scientists themselves are an achingly dull bunch, with the lettuce-limp Colin and Mary obviously the weakest performances on show. Jamie and Victoria aren't really suited to the material they're given. Ultra-modern Ben and Polly could have passed as supporters of Salamander, but I have a hard time believing these two would do anything but attract attention. A story like this (monster-less; arguably the true final pure historical of the black-and-white era, just a history that hasn't happened yet) has to rely on some sense of realism to live up to its ambition as a political thriller. Enter the Hansel and Gretel companions, who are so insignificant that they're not even in episode 4.

As an island in the superlative and otherwise monster-filled season 5 I find this story fascinating, and as a change of pace it does exactly what it sets out to do, and is invaluable as evidence of the creativity and variety the production team was capable of in this golden era of Who. That it is in the bottom half of stories from that season is a testament to the quality of the rest.