"Lost Souls" is an original BBC Radio 4 audio play written by Joseph Lidster and is a spin-off from the British science fiction television series Torchwood, itself a spin-off from Doctor Who. It aired on 10 September 2008 in the Afternoon Play slot as part of Radio 4's Big Bang Day which celebrated the switching on of CERN's Large Hadron Collider that same day. Andrew Marr introduced the audio play live from CERN. An mp3 version of the audio play was freely available until 18 September, when the play was released on CD and as a purchasable download.