Elisabeth Sparkle (Demi Moore), a former A-lister past her prime, is suddenly fired from her fitness TV show by repellent studio head Harvey (Dennis Quaid).

She is then drawn to the opportunity presented by a mysterious new drug: THE SUBSTANCE. All it takes is one injection and she is reborn – temporarily – as the gorgeous, twenty-something Sue (Margaret Qualley).

The only rule? Time needs to be split: exactly one week in one body, then one week in the other. No exceptions. A perfect balance. What could go wrong?