Check Out at the Check In/Walkthrough

The following is a walkthrough of the Check Out at the Check In mission in Grand Theft Auto: Vice City,

Walkthrough
Go to Escobar International Airport to the payphone inside and pick up the phone. After the call is done, get the sniper rifle that Mr. Black left for you at the drop point behind the potted tree to your right. Then, find the woman that's indicated and follow her with your scope. When she goes up to a man and asks the time, there's your target. When indicated, you should kill that man and take the briefcase he drops.

Run outside, get a fast car, and then drive to the Ammu-Nation in Downtown, and when you get there and step inside, the mission is complete. Be very careful and very fast, because you will be followed by a few black Admirals with men shooting Uzis at you; they can very easily pop your tires, so get away from them as soon as you can.

The player may easily evade the pursuing Admirals by driving behind the Vice City Transport Police building (beside the car park where the Admirals drive out and start chasing the player) and heading north or by driving north above the tunnel (by the curved runway) leading to Fort Baxter Air Base, exiting the area via Little Havana.

You can also use a helicopter to get away, which is recommended as it provides faster travel and minimal risk (You may leave your weapons behind as they will still be there when you go back). The nearest parked helicopter is a Maverick located at a helipad by the Freight and Cargo Terminal southeast of the airport. Remember, it takes 6 seconds to take off with a helicopter so if cops get near you get out and kill them before they drag you out of the helicopter and bust you.