This mission can be gotten from Michael's house. After a bit of convincing, your son decides to go on a bike ride with you, so go outside, get in the car and drive to the bike rental stand. When you get there, get on one of the bikes and you'll race Jimmy to the end of the pier. Note that if you cycle too much, your stamina will run out and you'll start losing health, so make sure you back off on peddling once in a while.
Once you get to the end of the pier, Jimmy will mention that Tracy is on the boat just over there, doing some movies. This angers Michael, so run to the edge of the dock and then dive into the water. Swim to the boat and go to the deck to watch a scene, which will lead to you being chased by two guys with guns.
Don't worry about the guys shooting at you and keep driving the jet ski. You should see a tunnel that you can go through, so take it and keep going straight. Just follow the path without making too many turns and you'll eventually lose them. Once you do, bring Tracey back to the beach where Jimmy will be waiting. After a short scene, the mission will end.