The Black Drop was the first of Jason Morningstar's Trail of Cthulhu adventures. It's available as a 40-page PDF or in the Out of Time compilation of adventures. In either format, it consists of a three-column, gray-scale layout with some nice artwork and a very usable layout although it's tough to use on a tablet.
As written The Black Drop is designed to be easily adaptable to either the Pulp or Purist style of play, depending on the mood of the table - all that it really takes is a few tweaks to the tone of the Keeper's descriptions and scene framing.
The Black Drop pays homage to horror stories set in cold, remote places (e.g., Beyond the Mountains of Madness and even John Carpenter's The Thing), without really being derivative of any of them. It takes place Kerguelen archipelago in the southern region of the Indian Ocean. Its locations and history are also based in reality – this includes the names of several notable NPCs on the islands. However, unlike real history, things in the Kerguelen Islands will take a much more horrific turn as the adventure opens.
The premise for the investigation has the investigators aboard a freighter steaming into Port Couvreux in the Kerguelen Islands. The French government has has decided to abandon its failed settlement in the remote islands, and the ship's crew and passengers have been sent to either aid in the colony's abandonment or are taking advantage of the situation to visit the islands one last time. Meanwhile, further down the coast, a mysterious German-funded expedition has arrived, likely for no good purpose (the adventure is set in the 1930s so we're talking about Nazi Germany here). As expected, the investigators quickly find themselves wrapped up in a sinister plot involving an ancient evil about to rise again, cultists, Nazis, and a battle to save humanity.
The investigation itself is fairly straight forward, with a variety of clues that ultimately will lead the group (hopefully) to the the climactic finish. To its credit, the investigation has a very flexible structure that will let players head in a variety of directions rather than being forced down a very specific path to the end. There's also quite a bit for the Keeper to define and flesh-out in order to make the adventure their own, tailoring it to the style and tastes of the group. That said, there's more than enough detail for a novice to run straight out of the book.
Similarly, the pregenerated characters that are included are a good fit for the adventure, but are left undefined enough for players to make them their own. However, unlike some other Trail of Cthulhu adventures, the pregenerated characters aren't quite as tightly integrated in to the story and therefore The Black Drop is easier to fit into an ongoing campaign, using player-generated characters.
I really like The Black Drop: it's a dark, bleak adventure with the potential for a mixture of investigation and action. While I'm more of a fan of the more Purist-style ToC adventures, that's more of a matter of taste and The Black Drop can easily be adapted for that style with a minimal amount of effort given the quality of the writing and the nature of the story, and thus The Black Drop is well worth investigating.