There is a security system plans exchange taking place at the top of Mile High Club construction site in Downtown Los Santos (the same place where the mission The Construction Assassination takes place). Lester is interested in the plans. When one of the players has collected the briefcase, the team needs to deliver it to Lester's warehouse in Murrieta Heights.
- Steal the briefcase.
- Deliver the briefcase to Lester's warehouse.
- Along with Sinking Feeling, this is a mission with no respawning if one of the players gets killed (presumably because a respawned player will be on the ground and have no way of getting back up to the briefcase).
- The mission's name is a pun - the phrase "High Priority Case" would usually refer to a court case, but in this respect it's referencing a briefcase.
- Helicopters are scarce around Los Santos, as Lester will not provide a helicopter to spawn. This makes the mission incredibly difficult to complete unless one already has a helicopter bought from either ElitasTravel.com or Warstock Cache & Carry.
- Merryweather helicopter pickups are available at rank 30.
- Helicopters do spawn at the Higgins Helitours helipad at Puerto Del Sol, but they might not be there on the first visit. If a helicopter is not there, drive back out and turn left towards the marina, turn round and come back. If a helicopter is taking off when you get there, drive up and wait as it will usually hover for a moment and land, unless you park on its designated landing pad or do something aggressive to scare the pilot off.