Express From Rome - S1.E8

The episode opens in Rome with a man entering a hotel room and telling the woman who's been waiting for him there that he's 'got them'. She says they need to hurry to catch the train. He tells her she'll have to go alone [he's been hurt]. When the woman arrives at the train, she bribes the conductor to give her another sleeper compartment. The compartment he gives her happens to have been booked by Rupert and Amy so the conductor gives them the woman's old compartment, telling them that the number they are reading on their reservation card as a 6 is actually an 8 so they have no idea they've been swapped. The compartment-swap leads to a case of mistaken identity and to Rupert and Amy's involvement in yet another adventure.