The film is set in Los Angeles on Labor Day in 1978: the last day of summer.
The singer, Bonnie, is refused a renewal of her contract and told to take a few months to write some new songs. She heads off in her car and ends up at Zuma Beach, a place she has good memories of. Her arrival causes a bit of a stir among the young men on the beach as she is a very attractive woman.
David Hunter arrives on his motorbike and is greeted by the parking lot attendant, Jerry McCabe. We learn that they have plans to hit the road together from tomorrow. David goes onto the beach and spots another motorbike standing beneath the lifeguard watchtower.
First scene with JD. We see him inside the lifeguard hut with a girl, Nancy. He is trying to seduce her but she is not too willing, wanting to spend some time together before consummating their new relationship. A chant of JD's name starts up outside and the pair go to investigate. JD takes up the chant, arrogantly assuming it is because of his prowess on the beach volleyball team and then spots his motorbike. It has been buried to the handlebars in the sand. Camera cuts to David who loses his grin when he sees Nancy with JD.
We meet a few more of the people on the beach. In particular, Norman, who tends to spout Shakespeare much to the dismay of his friends.
We learn that Nancy and David were an 'item' but that they broke up very recently because of his plans to go off with Jerry rather than stay and go on to college. She tells him that nothing happened between her and JD, but there is a sense of great rivalry existing between David and JD long before this day. A good quote from David: The only thing worse that being with a guy's best friend is being with JD.
Bonnie decides to build a sandcastle. Norman starts talking to her and ends up helping to design and build a massive sandcastle. The girl that Norman has fallen for comes over to help and they start talking. Slowly, others on the beach join in until a fair number are involved with building it and digging a large hole to act as a reservoir for filling the moat. When it is finished they have a opening 'ceremony' and let the water in the reservoir reach the castle moat.
The pleasure is shortlived as JD, who is playing throw and catch with a football, runs after a long throw, leaps, catches the ball but lands right on top of the sandcastle, demolishing it. Tempers run high but Bonnie defuses the situation by starting a sandfight with the remains.
The boys and girls form two parallel lines. Each girl has to choose a partner for the piggy back race. Nancy is first, but she chooses JD over David, causing David mor eanger. Bonnie chooses David. JD and David tussle during the race, elbowing each other.
Norman wins the race but David is livid. He has a go at JD to which JD replies: Sore loser, David. Always have been. Always will be. David challenges him to an 'arm' fight. This involves taking turns to punch each other on the arm. They take several turns with vicious blows but then end up in a scuffle on the sand and are dragged apart by the lifeguard.
The Malibu Beach volleyball team arrive for the final. JD tells Norman he is not needed, that they have enough players and Norman is upset. He speaks to David, telling him that JD refuses to let him play. David forces the issue and Norman is on the team. The teams are on equal standing and it is a tight game. It all comes down to the final match point and Norman misses the ball. The Malibu Team have won and race off victorious.
JD has a go at David because he feels it is David's fault for allowing Norman on the team. Norman decides to stick up for himself and punches JD, knocking him to the ground, calling JD a class moron. JD stands up but rather than fight back he offers his hand in friendship.
It is the end of the last day of summer. David has discovered that Jerry has been lying to him about the past as Jerry has been telling everyone that he used to be a big shot with millions, a yacht, fast cars but that he gave it all up to get out of the rat race. David cancels the road trip and plans to go straight to college. Nancy is happy and they are back together again.
With the sun starting to set, everyone grabs the lifeguard and drags him towards the sea. David looks round and sees JD standing some distance away with his arms around two girls. He calls to JD, inviting him to join in - and the rivalry comes to an end as JD runs over.
Additional Note: Kimberly Beck played opposite Michael Biehn Archive - the 1985 TV movie Deadly Intentions - in the role of Sally Raynor.