Whilst trying to return to London in the 1960’s, the TARDIS instead takes The Doctor, Ian, Barbara and Susan to France in the 18th century. The travellers realise that they’ve arrived in the middle of the French Revolution – a period in history that saw the French nobility and their supporters overthrown. Ian, Barbara and Susan are arrested as traitors, and locked in the Concierge prison, where Ian learns from a dying prisoner about the mysterious spy James Stirling. Barbara and Susan are scentenced to be executed, but are rescued before arriving at the guillotine. The Doctor takes on the guise of a senior revolutinary, and has to outwit Robespierre, the leader of the revolution, in order to try and reunite himself with his companions.