It starts off with a fun hook, find the daughter who has been missing for 100 years. The initial investigation was good, but it did seem a bit like a quest chain where each NPC hands the PCs off to the next NPC.
After that part, the plot gets a bit tenuous.
There are also some issues with the structure of the encounters once the PCs get to the point where they need to explore the wreck. If the group can't cast water breathing the adventure fails. At least have some sort of work around for parties that don’t happen to have this ability available to them. This happened one of the times that I ran this, so I had the Merchant Princes sell them potions of water breathing to allow the adventure to continue.
Why are merfolk warlocks pact of the fiend? This makes no sense thematically and also results in many of their abilities and spells being ineffective because they are fire based.
Why doesn’t Aremag have legendary actions? I can’t think of a single reason that there shouldn’t be a sidebar detailing additional abilities that Aremag has added to his stat block.
There are some good aspects to this adventure, but there are some parts that make no sense whatsoever.
[3 of 5 Stars!]