Tunnel of Death
It seems Derrick's old buddy Aiden O'Malley is going to rat him out. Aiden is being transferred in an armored van. He orders Niko to kill O'Malley before the convoy reaches their destination.
The mission starts with Niko ready to do as he is told, when Packie calls and informs you that he is doing the job with you. He also informs you that carrying out the mission as Derrick ordered is a bad idea. If the police knew that O'Malley was sprung from prison just to be executed, Derrick would be their prime suspect. They have to make it look as if they were O'Malley's allies.
Packie further tells Niko that he left a Biff truck in an alleyway that will be useful in the jail bust. He hid a rocket launcher inside as well. The first part of the mission is to pick up the truck which is now marked on your radar. Once inside, Niko calls Packie, who is out driving a truck of his own. He tells Niko that the plan is to corner the van as it is traveling through the claustrophobic Booth Tunnel.
You must drive the truck and enter the Booth Tunnel and travel a short distance inside where you will see two markers. You must park your truck across the two markers, making your truck a "perpendicularly parked" roadblock. The game goes to a cutscene. The convoy carrying Aiden O'Malley arrives and his halted by the truck. Packie arrives in his vehicle, and does the same as Niko, sandwiching the convoy between the two trucks. The police are more than suspicious by this point. One particular officer exits his squad car with the intent of instructing Niko to move his vehicle.
The cutscene ends with Niko outside the truck on the opposite side of the convoy, now armed with a rocket launcher. Now the fireworks begin. Gun down the officer approaching you, along with the dozen others nearby. Packie will assist you from the other end of the tunnel, but he will only take out one or two at best. Be careful with that rocket launcher; do not hit the van or Packie, otherwise the mission will fail.
Once the officers are down, Niko will hop in the driver's seat of the van, and Packie will sit in the back and babysit Aiden. You must now lose your wanted level. The trick is that your vehicle is as slow as a 56K modem, and your pursuers are seated in fast squad cars. Your one advantage is that the van is either bulletproof or nearly bulletproof (not sure which...) Anyway, exit the Booth tunnel, and try your best to lose the heat. One method is to lead the chase to Northern Middle Park. There, you can enter the subway system the same way you did in No Way Like The Subway. The police can only follow you for so long in there. Avoid the trains and drive until you have evaded the "wanted level" radius long enough for the police to call off the search. Once you do, flip a cookie (that means do a U-turn), and head back out the way you came in. Once the tracks lead you outside again, look for a gap in the railing, and you can exit through there. Here's the catch, you might flip your van. If you don't, you can move on.
After you have lost your wanted level, Niko relays to Packie that the van stands out, and they have to ditch it. You receive a new blip on your radar; it is a normal looking, four-seat sedan. You must now drive the van to where it is parked, and change your vehicle. (Man, if you count the one you drove on the way over to the Biff truck, then this is the fourth vehicle you have commandeered on this mission. Niko's just running through them isn't he?)
Once all three men are inside, you must drive to the cliffs. This is the easiest part of the mission. Just casually drive at your own pace, and follow the GPS to the mark on your radar. Along the way, listen to Aiden's requests of knowing who sprung him free, and enjoy Packie's endless death related innuendos he uses to answer him. The only danger on this branch of the mission is destroying your vehicle, so avoid flipping it, falling into the ocean, those pesky petrol containers that blow your car up if you run over them, et cetera et cetera.
Once you get to the cliffs, all three men exit the car and the game goes to a cutscene. Watch Aiden preach his gratitude on the edge of a very disappointingly short cliff. (Seriously, they wet our appetites with talking about "cliffs," making a large, Wile E. Coyote sized one come to mind, and it turns out to be just a ten foot drop?)
Aiden requests once more who put Niko and Packie up to springing him free, and to his dismay, "Derrick McReary" is the answer. Packie angrily condemns Aiden for his loose tongue and orders Niko to get rid of him. Packie gets into the car, and drives away leaving Niko with Aiden. (For goodness sake, Packie, was it to hard to wait five seconds and give Niko a ride home? Because you kinda left him transportationless...)
Anyway, the moment you have all been waiting for. With Aiden still standing on the ledge of the hill...okay, fine...cliff, you must simply shoot the Irishman and his body will roll down the hil, uh, cliff, and into the ocean.
Mission over! You are now left standing at the murder site, and if you did not stall in killing Aiden, you can still see Packie's car driving away from you. What a jerk.
Anyway, you've completed Derrick's strand and were awarded $7,500.