"GS Wonderland" begins in the summer of 1967 when a brash and determined young singer Miku (Kuriyama Chiaki) goes to Tokyo with dreams of becoming an entertainer. Unfortunately, and because of the "GS Boom" all the record labels just want all-male groups and refuse to sign her up as a solo act. The Executives at Fine Records are one such company. CEO Matsuda (Kishibe Jukichi) has tasked one of his managers, Sasaki (Sugimoto Tetta) to establish a new "GS Group" in three months time or else. Sugimoto entrusts his chief talent scout, a washed-out, former rockabilly singer, Kajii Rousuke (the hilarious Takeda Shinji) with finding the group. By sheer dumb luck he stumbles upon a trio of fledgling musicians practicing on the rooftop of an apartment. Guitarist/lead singer Masao (Ishida Takuya), drummer Syun (Mizushima Hiro) and high school student and bassist Kenta (Asari Yosuke) have all been the victims of and had been ridiculed and humiliated by the reigning GS Group of the time "The Knuckles" led by the arrogant Hasegawa Tajio (Takaoka Sosuke), who continually misinforms other naive musicians that "the Beatles" are recording/vacationing in remote areas of Japan. Kaijii reports his discovery to Sasaki but he says that all the other groups have a keyboardist and that they need one to complete the group. In desperation Kaijii recruits Miku into the group but makes her conceal her gender by pretending to be a boy named, Mick (Mick Jagger?). They debut as the "Diamonds" but due to a lackluster song, a misspelling of their band name on the record, and no real gimmick, they only manage to sell a meager 23 copies of their album (most of which were bought by the band themselves). Sasaki and his boss Matsuda soon come up with their loopy gimmick - having the band dress up in tights, boots and Victorian style frilly outfits. Renamed the "Tightsmen" they debut with a more polished song. While the rest of the band look silly in the new uniforms, it manages to make Miku into an androgynous knockout (think Prince Oscar from the famous "Rose of Versailles" girl's comic of the 70s) and she soon becomes the heart-throb of the group and propels the group from obscurity into fame. However, can the group manage to continue to hide her secret from their fans and more importantly with the advent of "Psychedelic Rock" have they attained stardom too late in the game?