The gang is shocked by the death of a popular professor. As a result, Zack adopts a new attitude towards life by seizing the day and taking more risks.

Just as Zack and Kelly are getting pretty close, Kelly is accepted to the Semester on the Sea program, which involves a three-month cruise. Zack doesn't want Kelly to go, but she feels it's an opportunity she can't pass up. Zack tries to get accepted into the program as well, but none of his schemes work. He tries to get Screech to quit the program by scaring him, but that backfires and Zack impulsively makes an important decision. Meanwhile, Slater feels guilty when he sees another girl behind Alex's back and gets confronted by Leslie.

As Zack and Kelly make plans for their wedding, they get a surprise visit from their old friend, Lisa Turtle. However, since Alex and Lesley also want to be Kelly's maid of honor, the competition between the three of them ensues. Meanwhile, Slater doesn't approve of Zack's decision and turns down his offer of being the best man. Screech agrees to take his place with predictable consequences.