You should get an e-mail from Lester who says you need ten bags of E. You can find a seller at the south end of Broker, though don't be surprised if you get sucked into a bust—we did. When you've got the goods, make your way to Lester's pad for the lowdown on the mission.
There's a motorcycle nearby that you need to hop on and ride over to the gang hideout by the given time. You don't need to be very fast, so take it easy in order to keep the bike in once piece. When you arrive at the hideout, you'll be told to ride in style and chase off the gang's rivals. To start, do a burnout and then peel ahead to launch off the ramp in the back alley. There are a couple of waypoints to hit directing you to the next.
You'll follow a number of waypoints before being lured into a back alley that's crowded with rival gangsters. Ride around and shoot 'em up to wipe out the lot and then rejoin the waypoint train out of the alley.
After hitting a few more waypoints you'll be given some red dots on your radar that represent rival gangsters riding around the city. You need to catch up with them and kill two of the three, leaving one to tell the tale. Catching up with them isn't super easy—they're pretty quick—but be patient and don't let them get too far away. You'll eventually get 'em, at which point you can gun them down.
Finally, you'll get a notice to meet with Lester and he'll hook you up with some explosives. Grab the gear and get back on your bike to drive to the park (expect a ramp to jump off of). Walk to the base of the globe and plant the bomb. You have to complete a mini-game of Simon Says to arm it. After a quick cut scene, the mission ends.