Catalyst

Catalyst is a mission in Grand Theft Auto: San Andreas, given to protagonist Carl Johnson by fellow Grove Street Families member Ryder from his home in the Ganton district of Los Santos, San Andreas.

Plot
The mission begins with Carl going to visit Ryder, who is making his own "water" after he couldn't find it in his backyard. While Carl and Ryder are talking, Tenpenny and his accomplices drop by to inform the two that there will be a army munitions train passing through town shortly, and that enemy gangs such as the Ballas will try to raid the train.

The two immediately depart, arriving at the train only to find the Los Santos Vagos have ambushed the train first and are attempting to offload munitions fighting the Grove Street boys. Once the Vagos are dead, the Ballas show up and try to take the train. Though the OG's will succeed to protect the train from the Ballas, and when it starts up, gradually leaving the area of the ambush. Not wanting to lose the munitions, Carl jumps on the train. Ryder is now in the back of his Picador, who waits with a Grove gangster driving behind the train, with Carl throwing some boxes to him. After acquiring sufficient munitions, the two are pursued by the police. They got to the Pay 'n' Spray to lose the cops, and goes back to Ryder's home.

Transcript
Carl Johnson: Hey, Ryder? What the hell you doing?

Lance "Ryder" Wilson: Nigga, I couldn't find that wet I buried, so I'm making my own. It's easy, fool.

Carl: Oooh! That's strong. Man, don't do that! You'll sauté the both of us.

Frank Tenpenny: Morning boys!

Ryder: Man, who you calling a boy, fool?

Tenpenny: What should I call you? Midget?

Eddie Pulaski: How about prick?

Tenpenny: Prick...

Pulaski: Yeah, prick works.

Ryder: Man, fuck you.

Tenpenny: Bitch, get outta here. Mmm... Smells good. What's cooking? Where's mine?

Ryder: Man, just chill out, a'ight. Move. Here. Don't be sweating me, motherfucker.

Tenpenny: Mmm, my wife loves this stuff, man.

Pulaski: *laughs*

Tenpenny: Anyway, there's a train gonna make an unscheduled stop just down the way. Its got a, how you say, "little something something" on board for you boys. Square business, man.

Pulaski: Catch you later, homeboys.

Ryder: Asshole.

Tenpenny: Oh Carl, try not to kill any more respected police officers. Please?

Pulaski: Crime has certainly gone up since you got back, kid.

Carl: Just doing my part for the community.

Tenpenny: Your train's gonna be their in five.

(Carl and Ryder, once gone back to Ryder's home)

Ryder: Damn, homie, your stuff was tight!

Carl: You too, homie!

Ryder: LB's coming over to stash the shit.

Carl: Okay, later then.

Ryder: For life, CJ, for life - you heard?

Reward
The reward for this mission is increased respect. The mission Robbing Uncle Sam is unlocked.