The movie follows Tree Gelbman (Jessica Rothe), a college student who keeps reliving the same day over and over again. Every day is the same: she wakes up to the song "Happy Death Day" and is killed by a masked killer.

Tree is a shallow and selfish college student who doesn't really care about anyone but herself. On her birthday, she wakes up to find that she has died. But instead of moving on, she wakes up again to find that it's the same day all over again.

As Tree tries to solve the mystery, she starts to develop feelings for her professor, Dr. Gregory Butler (Charles Aitken). She also becomes more empathetic towards her friends and starts to care about them.