Gwen recovers an errant piece of alien technology which provides glimpses into the past. While experimenting with the device, Owen witnesses an horrific rape and murder which has gone unsolved for more than four decades. As the rest of the Torchwood team investigates the machine's origins, Owen teeters on obsession with bringing the killer to justice.

Helen Raynor had been a script editor on the first two seasons of the revived Doctor Who series when she was invited to contribute a script to Torchwood. Raynor had also written for Brief Encounters, as well as for radio. The intent was that Raynor's script would be held back in case of emergency, or else for a hypothetical second season of Torchwood, but the production team was so impressed by Raynor's ideas that the episode was added to the season schedule under the title Ghost Machine.

Ghost Machine formed part of Torchwood's second recording block, paired with Greeks Bearing Gifts. It was directed by Colin Teague, whose other credits included Holby City and London's Burning. A last-minute rewrite had to be undertaken on the story's opening chase sequence. Originally, this would have featured Jack, Owen and Gwen pursuing Bernie Harris through the streets of Cardiff. However, John Barrowman twisted his ankle while filming on the Hub set just a few days before, preventing him from running. The scene was therefore rewritten to have Jack show up partway through in the Torchwood vehicle.

• Forthcoming.