This is a spoileriffic review of Slow Boat, by Peter F. Jeffrey and Mark Morrison, from Fearful Passages.
On the whole, I found it a promising scenario with at least one intriguing NPC and potential for running an unusual campaign, though with a few backplot holes and a structure built around strong events that might be tricky to use effectively.
The scenario begins with a decent overview of canals, canal boating and associated matters, which looks very solid to me for use in games. I was also pleased to see that it then lays down what's really going on before moving into what Investigators will see. I certainly can't say it's the objectively best way to lay out scenarios, but I tend to find it easier to follow the thread if you know the backstory already, rather than picking up pieces of it mixed in with the clues. It's a short, efficient explanation before the main scenario begins.
Investigators are called in when an heiress goes missing in strange circumstances, leaving her occultist lover under suspicion. In fact, a necromancer from the distant future opened a portal that they blundered into. The occultist, Marcus Raven, managed to convince the necromancer he was a sorcerer, and make a deal to bring back sacrifices in exchange for Aline's life. He will try to draw the Investigators into the portal, hoping to win the day one way or another.
This is a fairly short part of the scenario, but could easily take some time. Investigators may need to travel to England; they have to meet up with the PI currently on the case, seek out Raven, and begin traversing the canals. The latter is a slow process, but can be made quite interesting with questioning, sneaking looks at Raven's occult library and disturbing memoirs, and being questioned themselves by the PIs who follow the boat. The Investigators are very much running a parallel investigation - though the police are handwaved away. If players enjoy that sort of thing, there's also interesting scenery to traverse, locks to handle, and other boat-related activity. They can learn something about handling a boat on the way (Pilot [boat]). They can also take a detour to examine the mummified body the couple found in the canal.
The boat contains both a copy of Nameless Cults and an Elder Sign, but neither is tied into the scenario. This could be a good opportunity to gently introduce both into your Investigators' party, for future use, or a creative player might find a use for them. You may need to keep an eye out to make sure they're not misleading the players, though. Raven's memoirs are a Mythos tome (some memoirs!), but could really have done with some fleshing-out so Keepers have something concrete to say about them. The same applies to discussing his previous exploits, or his relationship with Aline.
At this point, the Investigators may decide they've fulfilled their obligation and drop the case. More likely, they'll want to see the scene of the disappearance, even though it's not part of their contract. If the Investigators do drop the case, more mummified bodies will emerge from the canals over the following days, and eventually, Raven will come and tell them the truth. Presumably, they can also compel him to spill the beans, by fair means or foul.
One way or the other, Investigators will end up headed to the canal tunnels, either as dupes of Raven (undoubtedly suspicious, but ignorant of what's really going on) or prepared for a nightmare expedition. The boat, powered by the remaining magic orb, passes through the portal to the dying world (a version of Clark Ashton Smith's Zothique), full of grimness and the undead. For some reason the scenario assumes the Investigators will let the ubrupt nightfall, the unfamiliar stars and the lifeless landscape pass without comment, and proceed upriver for an hour or so, passing through two locks of bizarre design, until they see their first zombie and Raven finally spills the beans. Luckily, you can have him explain as soon as they arrive, without doing any harm. The landscape, and the necromancer's tower, are suitably impressive without being purple. As may be expected, or not, the necromancer's initial civility disguises an ambush.
The option to have the PI and policeman stow away on board is nice, offering a few different options depending on how things play out. They could simply become replacement PCs, or a creative Keeper might let the players cut to them while the party's imprisoned. Perhaps they can find a different way to free the party - maybe Raven guessed they were there, and left them a message and an artefact to use? Or perhaps they'll go off exploring and go mad, be captured and experimented on, or otherwise have fun.
At this point, the scenario has two very divergent forks. It's possible for the party to simply kill Thathmuor outright, at which point his minions wander off, they can ransack the tower (or not; but come on...) and head home. Well, possibly. Though the scenario doesn't discuss this, if they kill Thathmuor there's a very real risk of them ending up captives of Valchrek, his rival. More on this later...
What's more likely, however, is the scenario's intended path, which has them captured and imprisoned underground. Raven claims he has a secret plan at work. Aline, now a shambling liche, eventually shows up to bring them a lamp. She turns out to have exactly enough self-control to champ at her bit, but not quite enough to destroy herself, and obliges Raven to set her on fire, leaving him useless for the rest of the game but leaving the door open for their escape.
Luckily, at this point Raven's plan kicks in, and an enchanted Hand of Glory he displayed earlier has unlocked the tower's magic door, allowing the rival necromancer Valchrek's forces to invade and cause a distraction. In the confusion, they can steal a magic orb to power their return trip, and flee. They need to pilot the boat - or at least a boat - back to the portal, luckily ignored by all the liches heading to reinforce the tower. Of course, if Thathmuor is dead by this point, Valchrek could easily seize the tower, its valuable contents, and indeed the Investigators... though you'd have to improvise the result yourself. It's essential that the Investigators get an orb in order to escape, so Keepers need to be very careful to make them aware of it, unless they're planning something very different. In theory, though, you can get the comatose Raven to mutter something.
They may be ambushed en route by Valchrek's forces, as part of a double-cross. They should be able to either fight or race their way to the portal, where "the investigatorsâ€™ survival is entirely dependent on whether they remember to take a temporal vortex egg from Thathmuorâ€™s tower. Without one, they are doomed." With one, they can return to their own time, where they're left with the problem of what to tell the police and Aline's father. They may also be wondering how to explain the disappearance of Raven, and any deceased Investigators, while they were known to be on a boat together under police observation.
As happens fairly frequently, the conclusion of the adventure doesn't actually close the case. They're hired to find Aline, but unless their employer's very credulous, he's not going to buy the true story. One wonders how it is that Investigative teams ever build up a reputation that gets them hired by millionaires, when this is the sort of result they produce...
...to be continued (too long for a single post)