"The Staircase (Mystery)" is the second single released by British rock band Siouxsie and the Banshees. Issued in the UK by Polydor Records in 1979, the track was written by Banshees members Siouxsie Sioux, Steven Severin, John McKay and Kenny Morris and produced by Nils Stevenson. The B-side of the single is a cover of the T. Rex song "20th Century Boy"