The Assassin missions are a series of side-missions included in Grand Theft Auto IV. The missions are unlocked after you complete the mission, "Truck Hustle" for Phil Bell. Niko recieves a phonecall from someone called, "The Fixer", who informs Niko he can call him to complete hit-contracts for decent money. For 360 users, complete every mission to unlock an achievement.
After Niko recieves the phone-call from The Fixer, he is directed to a telephone in in Alderney, which is shown as a target icon on the map. After you step into the marker, Niko will call The Fixer and recieve one of the randomly assigned jobs.
After each phone call, Body Armor and a mission-specific weapon will appear on the other side of the fence from the phone. It's helpful to collect this before heading to your target.
 Mission - Migration Control
The Fixer wants you to eliminate a target on top of the Booth Tunnel in Alderney City. Take a cab to your destination. When you arrive, head east towards the sound of the helicopter, until you can see the helipad.
The easiest way to complete this mission is to equip the RPG and launch a few rockets into the helicopter. Make sure the red blip has dissapeared from the radar, as the target may still be alive. If so, move closer and finish the job.
 Mission - Bailing Out For Good
Take a cab to your destination, the police station in Leftwood. Your target is being escorted to a car. Use an RPG or grenades to take car of the target, then walk and talk as Niko calls the Fixer to escape the Wanted Level.
 Mission - R.U.B Down
Jack a fast vehicle and head to the targets in the Acter industrial park. You will find them in an alley between a police station and the Terroil plant.
There are two ways to complete this mission easily. Simply plough through the alley with your car or fire off an RPG towards the bikes.
 Mission - Derelict Building
Go to the targets, three men, in an abandoned building in Northern Alderney. They're located on seperate floors throughout the building, and each floor contains two or three armed gunmen. Work your way up through the building, eliminating targets and bodyguards as you go. Take cover on each floor to avoid being shot to pieces and watch your head as you ascend each ramp to the next floor. Try entering in first-person aim to pick off any gunmen. Once the mission is complete, leave the area to get rid of your Wanted Level.
 Mission - Taken Out
Go to the target's location and you will see a black limo, your main target, flanked by two SUVs. The second you show any act of agression, including bumping into one of the cars, they speed off. A simple method is to get a block ahead of them, or wait until they hit trafffic lights, then blow up the limo with an RPG/grenade.
 Mission - Hook, Line And Sinker
The target is on a boat on the Northern mouth of the West River. Make sure you have a sniper-rifle before you set off. Go to the shoreline and use the sniper-rifle to pick off the target, one of two men in the boat - marked with a red arrow.
 Mission - Industrial Action
You have three targets in the refinery at the Acter industrial park. When you arrive, work your way up the metal stairs near the main road. Follow the catwalks to the very top tier. From her you can snipe all the targets, located on an adjacent building.
 Mission - Dead End
Jack a car and head to the target. As you arrive, a Patriot speeds away. Follow the getaway Patriot into a nearby alley. The occupants will exit the vehicle and head into a loading bay. As you enter the alleyway, a second car pulls up. Take out the men in this car, using grenades or an assault-rifle to get it done quickly. Then kill the remainder of the men in the loading bay to complete the mission.
 Mission - Water Hazard
Take a cab to the target. The cab will drop you off at the perfect spot on the pier. Run south towards the bulkhead and aim at a nearby sailboat in the water. Snipe the target onboard to finish the mission.