"Zero Hour" is the twenty-fourth and final episode of the third season of the American science fiction television series Star Trek: Enterprise; the seventy-seventh episode overall. It first aired on May 26, 2003, on the UPN network within the United States. Set in the 22nd century, the series follows the adventures of the first Starfleet starship, Enterprise, registration NX-01. Season three of Enterprise features an ongoing story following an attack on Earth by previously unknown aliens called the Xindi.