San Francisco 1967. A place of love and peace as the hippy movement is in full swing and everyone is looking forward to the ultimate festival: the human be-in. Summer, however, has lost her boyfriend, and fears him dead, destroyed by a new type of drug nicknamed Blue Moonbeams. Her only friends are three English tourists: Ben and Polly, and their mysterious guardian and friend the Doctor. But will any of them help Summer, and what is the strange threat posed by the Blue Moonbeams?