From a riddle-speaking butterfly (Robert Klein), a unicorn (Mia Farrow) learns that she is supposedly the last of her kind, all of the others having been herded away by the Red Bull. The unicorn sets out to discover the truth behind the butterfly's words. She is eventually joined on her quest by Schmendrick (Alan Arkin), a second-rate magician, Molly Grue (Tammy Grimes), a middle-aged woman who dreamt all her life of seeing a unicorn, and the gallant and loyal Prince Lir (Jeff Bridges). Their journey leads them far from home, all the way to the castle of Lir's adoptive father, King Haggard (Sir Christopher Lee).