Back to Sid's filmography: This is a re-scripted version of the first in a four part series on the history of cave diving, which was based on Martyn Farr's book The Darkness Beckons. It reconstructs the early attempts by Jack Sheppard and Graham Balcombe to pass the two sumps in Swildon's Hole and by Jack Sheppard and Penelope Powell to pass the first sumps of Wookey Hole in the 1930s and 1940s using pumped air. It then reconstructs Balcombe's dives in Keld Head during the war years using rebreathing equipment. After the war, the Cave Diving Group was established, and Bob Davies and Don Coase used fins and rebreathing equipment to progress further in Wookey Hole, but Gordon Marriott lost his life returning from the Ninth Chamber. The film features interviews with Graham Balcombe. The divers involved in the film included Geoff Crossley, Ken Pearce, Peter Eckford, Bob Cork, Dany Bradshaw, Dave Turner, Bob Drake, and Charles d'Archenburg. It was originally shown on BBC One on September 25 1989.