Sputnik Sweetheart is a novel by Haruki Murakami. It is a literary mystery about unrequited love and loss. The 25-year-old narrator, referred to only as "K," is in love with his best friend Sumire, but Sumire is in love with an older, married woman named Miu. When Sumire goes missing from a Greek island, Miu calls K for help finding her; he discovers in the process that her disappearance may be related to a strange story from Miu's past. The novel considers themes related to love, dreams, and the unknown.