Largely improvised by director Rob Reiner and his cast, This is Spinal Tap looks and sounds like a "real" documentary, with Michael McKean, Harry Shearer, and Christopher Guest thoroughly convincing as David St. Hubbins, Derek Smalls, and Nigel Tufnel, the key members of a going-nowhere British heavy metal band called Spinal Tap. The "group" started as an informal skiffle band, eventually maturing into an R&B act called the Thamesmen (their hit was "Gimme Some Money"). After going through a psychedelic period with "Listen to the Flower People", the band mutated into Spinal Tap, a hard rock outfit responsible for such albums as "Intravenous DeMilo", "The Sun Never Sweats", and "Bent for the Rent". This Is Spinal Tap finds them in the midst of their first American tour in years as they support their new LP "Smell the Glove", with filmmaker Marty DiBergi (Rob Reiner), who specializes in TV commercials, on hand to document the occasion. Just about anything that can go wrong does; shows get canceled, stage props go wrong, wireless guitar pickups start broadcasting air-traffic reports, no one shows up for in-store appearances, David's girlfriend tries to take over the band, they wind up billed second to a puppet show at an amusement park, and the group teeters on the verge on breakup. Despite the ridiculous crises that befall the band and their hilariously wrong-headed music (including such classics as "Tonight I'm Gonna Rock You Tonight," "Big Bottom," and "Sex Farm"), the movie manages to laugh both at and with its subject - no surprise, since McKean, Guest, and Shearer all played in bands at one time or another; Shearer even claims that the "kick my ass" sequence was inspired by a disastrous in-store appearance by his comedy group The Credibility Gap. After the film's initial release, McKean, Guest, and Shearer did a short club tour as Spinal Tap; the "band" reunited in 1992 for a new album, "Break Like the Wind", followed by a full-fledged tour and TV special, The Return Of Spinal Tap.