9-year-old Catherine is used to setting aside her own needs when taking care of her younger sister Sophie who has multiple impairments. But one day Catherine suddenly finds herself in an underwater dreamworld where Sophie is a giant pink unicorn called The Dream Master. Together, they set out on an enchanting adventure where they meet all sorts of magical creatures: talking toys, rapping mermaids, and much more. The many hardships bring the sisters closer. Outside, in the real world, they can’t communicate, but through imagination Catherine discovers a way to communicate with her sister. And for the first time she feels that she finally got the little sister she always wished for.