Storyline is up to you to discover.
This is 1st out of several Chapters.

Remember:
Due to bug crash, leave car before entering certain checkpoints.

Failure in scripting leads to game crash in last mission so DON'T ENTER AMMUNATION! Proceed back to field after entering checkpoint otherwise you'll crash 

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This storyline can be found on GTAForums, so search a bit if you want ;)
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Any questions regarding this?
GTAF: http://gtaforums.com/user/807253-nellesrb/
DYOM: http://dyom.gtagames.nl/profile/4577