On this page of our game guide to Mafia Definitive Edition, you can find a detailed description of mission 12 - Great Deal. By reading our walkthrough you will find out, among other things, how to survive an ambush at a multi-storey car park and how to properly escort an alcohol truck on its way to Salieri's warehouse.
Drive to the Parking Lot
Get in the car in which Paulie and Carlo are already sitting and head towards the multi-storey Parking Lot in the Central Island area.
Once you get there, drive inside and reach the top level. Park the car in the marked spot.
Survive the ambush
After watching the cut-scenes, keep staying behind the cover. Just lean sideways for a brief moment so you can fire at the gangsters. Defeat all your opponents and go back to Gates to determine how hard he's been hit.
Escort the truck
While running through the underground parking lot, you don't have to worry so much that the truck will get destroyed. It will remain behind while Tommy and his allies move forward to kill more gangsters.
Expect more opponents at every next level of the parking lot. It is important to take cover behind subsequent columns in order to safely shoot at your enemies. Hiding behind parked cars is more risky because they may explode after they get destroyed. Also, check out small rooms along the way, as they may contain First Aid points and ammunition.
On one of the lower levels, an explosion will occur. Flames will prevent the escorted truck from driving any further. After dealing with the nearest opponents, choose the right door shown in the picture.
Watch out for at least one opponent along the way. You'll also find a crate with grenades and a first aid point. Reach the valve and activate the sprinklers.
Continue to break through into the lower floors of the parking lot and expect to come across even more enemies. Just like before, look for opportunities to take cover behind the columns of the parking lot. You can also use grenades to destroy vehicles behind which enemies are hiding.
Once you reach the lowest level, find the first aid station and talk to Sam.
After you get into the vehicle, leave the parking lot, and start following the truck. You must attack enemy vehicles. In addition to controlling the car, take your pistol and fire at the gangsters cars that are trying to stop the truck. Also, if you can get close enough to them, you can press the ram key.
In the further part of the chase, you will have to drive on rough terrain through Hooverville. Focus on flawless driving and don't collide with any indestructible obstacle.
Continue attacking enemy vehicles appearing in the path of the truck. It must reach Salieri's warehouse. Drive into the warehouse to launch a new cutscene and complete the mission.