The Doctor and Charley decide to take a well-deserved break from the monotony of being chased, shot at and generally suffering anti-social behaviour at the hands of others. And so they end up in Venice, well into Charley's future, as the great city prepares to sink beneath the water for the last time... Which would be a momentous, if rather dispiriting, event to witness in itself. However, the machinations of a love-sick aristocrat, a proud art historian and a rabid High Priest of a really quite dodgy cult combine to make Venice's swansong a night to remember.