Back to Sid's filmography: This is a re-scripted version of the fourth in a four part series on the history of cave diving, which was based on Martyn Farr's book The Darkness Beckons. The film consists of some reconstructions, and some film of actual exploration. The divers involved in the film included Mike Wooding, Geoff Yeadon, Jim Abbot, Rupoer Skorupka, Oliver Statham, Ian Watson, Martyn Farr, Malcolm Stewart, John Shaw, Rob Parker, and Geoff Crossley. Sites that appear in the film include Keld Head, Boreham Cave, Wookey Hole, Agen Allwedd, and Gavel Pot. In interviews, Geoff Yeadon recounts the Dead Man's Handshake incident with Jochen Hasenmayer; Farr discusses the circumstances surrounding the death of Roger Solari; and Rob Parker discusses the impact of multi-gas rebreathers. It was originally shown on BBC One on September 29 1989.