The Cardinal has sent for reinforcements against that 104-gun ship you found, but by the time they are here, it will be underway. Someone needs to stop it before it's fully repaired.
- Sink the 104-Gun Ship
- Go the the Escape Point
For all intents and purposes, this mission is actually a high-level copy of another mission you might already have done in your starter town: The Not-So-Great Escape.
The setup is as follows: the immobile (but fully armed, unless you attack it immediately) pirate SoL - a level 50 'Invincible' First Rate - will be ahead of you at the end of a small bay, with most of its armor and structure gone (unlike the cannons, these won't be repaired much during the mission). It will be guarded by two escort ships, both around level 38-40. As soon as you get within firing range (even if you approach from a dead angle), four more enemy ships of similar level will spawn around the exit point and start to come after you.
So do not approach the SoL at first, but let the guards come to you and defeat them without getting in range of the SoL. Doing that actually lets you meet the 2nd objective (get to the exit point) before the first one (kill the 104-gun ship). As soon as you've killed the two guards, sail over the escape point (this might already have happened during the fight, in which case the objective will be met already). After this it's time to go for the kill.
You best approach the 104-gun ship while hugging the nothern coast line of the bay. This way you will keep out of its cannon sights and can get to within a few hundred yards of it (stop before the stern guns can hit you). Even though the 4-ship ambush has by that time appeared already and is coming after you, you should still have plenty of time to sink the SoL and finish the mission before they can get to you.