Objective: Track the auction briefcase and watch for hand-offs
Objective: Follow the briefcase unseen

A soon as the man takes the briefcase keep your eyes on it as its passed from person to person. Go back up the stairs and watch from there, where you get a good view and you wont be spotted.

Objective: Tail the boat carrying the briefcase
Objective: Locate the briefcase unseen

When the briefcase arrives near the pier, get in close and check out the motorbike close by. once the last person moves away, jump on the bike and follow the boat on land.

When the boat arrives remember you need to find the briefcase without being seen. Move the platform and it will rotate to the building. Youll soon see the briefcase and its now time to get it.

Objective: Infiltrate the marina to get the briefcase
Objective: Escape the marina

Get on to the far left of the platform and swim to the ladder on the left of the garage door. Youre now on the north side of the building. You need to head over to the east side of the building where there are three men. Two are stationary and one is patrolling. Get access to the camera to see their locations. Move up the stairs to the main area and wait for the guard on foot to move south. Now move closer to the briefcase and stop near the woodpile and hide until the on-foot guard comes back. You wont make enough noise to alert the guards (unless you start shooting without a silencer). Watch the guards and when theyre facing the opposite way head straight for the briefcase.

Once you have the briefcase escape the area the same way you came to complete the mission.