In my campaign the atmosphere on the Sea Wyvern is getting tense and the PCs are adding to the tension. In the beginning the PC captain did her best to keep tension under control, but she has been neglecting that lately and gone complacent. She thinks she has everything firmly in hand. Also, PCs have been involved in a series of mysterious incidents where several NPCs have disappeared under questionable circumstances. The PCs have explained away all these incidents, with high bluff checks, but these explanations were even more worrisome than the events that they were meant to hide. The PCs have been telling stories about people disappearing in mysterious cursed tempels dedicated to ancient Olman gods, about attacks by demons and mysterious undead and about Olman plotting to murder innocent NPCs.
And one of the PCs together with Skald shot a (savage) albatross.
The crew is muttering and getting more and more superstitous after hearing all these stories. The final incident was that the captain accused an Olman passenger of killing one of the other passengers. The Olman confessed, but his behavior was strange and he was screaming about a curse (he was under the influence of a very subtle magical effect). The captain decided to let him walk the plank.
The named NPCs who are really getting worried, are Skald, Avner, Amella and Lirith. Amella notices from her earlier experiences aboard ships that something is brewing, and is worried that the captain cannot control the situation anymore. Avner is angry with two of the PCs, since one stole "his" girl, and the other is downright rude against him all the time. Lirith has allied herself with Avner, since he is rich and the PCs have been totally ignoring her so far, dismissing her as unimportant. And Skald has begun to worry that some of the PCs might be evil (though he does not have any hard evidence, and one of the PCs he does not suspect, is his friend). Then there are some nameless crew members who are simply superstitious, especially about the albatross.
There is another named NPC (of my own making) who knows for a fact the truth behind one of the incidents, because he was there. He knows the PCs murdered an NPC, and is even an accomplice to that murder. It was necessary, since it was a dangerous and evil NPC. However, this named NPC is getting worried, because he suspects that the other incidents on the ship also have to do with getting rid of undesireables, and fears that it will soon be his turn, because he knows too much about the PCs.
And then there is father Feres, who is emotionally manipulated by one of the PCs. She is seducing him for her own ends, and certainly not out of love. She does not do anything to hide it from the others, and people are beginning to notice. Moreover, the Olman who was forced to walk the plank, was a competitor of father Feres for her attentions, and is now conveniently gotten rid of.
Contacts with the Blue Nixie are also not very good at the moment, as there is friction between one of the PCs and three of the Jade Ravens (since the PC is flirting with Liamae).
For me as DM this feels like an explosive situation. The question is when and how I am going to let this explode.
Ideas would be very much appreciated, especially if someone has had a similar situation (a mutiny) on the Sea Wyvern. How did it go?
If the NPCs are strong enough to mutiny and win, they could maroon the PCs on or near the beach where "Here There Be Monsters" begins. Or if a struggle erupts at this juncture, it could doom the PCs' efforts to control the ship and make the shipwreck inevitable.
If the NPCs believe the PC captain is putting the ship in danger through bad decisions or poor seamanship, it would certainly be plausible for them to mutiny in the storm.
They could also cut their way out of the kelp patch and leave the PCs behind after the PCs defeat the Mother--they might leave a small boat behind just to avoid feeling as though they've murdered the PCs.
It would probably be a good idea to make a little roleplaying/encounter flow-chart to plan how to give an escalating series of signals that a mutiny is in the works, and some idea of what responses might be effective in quashing the mutiny at what juncture. A PC overhears mutinous talk at the scuttlebutt--if the PCs take drastic action to punish the mutineers and restore discipline does this squelch the uprising or fan the flames of resentment and lead to something worse later? That sort of thing. If you don't give some warning signs and give the PCs an opportunity to act on them, the players might feel railroaded.
Also, depending on the number of active mutineers and whether they are able to catch the PCs by surprise, a mutiny might well not succeed even if it's twenty crew members against four PCs.
Avner might be a good leader for the mutiny. That would give the PCs an excuse to execute him summarily, but there would be later repercussions--Avner's uncle could easily suborn some witnesses from the crew into giving false testimony that Avner was unfairly accused and unjustly executed.
Some sources for ideas on how a mutiny might work:
Robert Louis Stevenson's "Treasure Island" (I'm sure there's a movie version or three if you don't want to read it--but it's a pretty quick read and a great classic--the expressions of tension and distrust on the ship between officers and crew are a good model for how to foreshadow the mutiny.)
Herman Wouk's "The Caine Mutiny" (novel, adapted into a movie starring Humphrey Bogart as Capt. Queeg--modern setting, but plausible psychology, and the mutiny takes place in the middle of a hurricane that threatens the safety of the ship).
"Mutiny on the Bounty"--I think there are a couple of movie versions of this, plus the real-life historical tale--there are several historical accounts and you could get a synopsis from Wikipedia.
"Mutiny on the bounty" actually gave me the idea. It gave me the feeling a mutiny always starts with an execution.
I also have a copy of Treasure Island, and have recently seen a stage version of it. This was also a source of inspiration.
You are right that the PCs should see it coming. But they already do in a way. After the session on Friday one of the players commented: "O no, this is it! We went too far!"
They wanted to keep the execution factual and businesslike, but they like melodrama and it became much too dramatic. That is where it probably went wrong.
I have made a table with all the NPC attitudes, which I check and correct after every session. Needless to say, NPC attitudes are worsening (some downright hostile).
It sounds like you have a similar situation. Superstition also plays a role in both cases.
My PCs not only left for shore and came back with loot, but every time they left for shore, the NPC who had accompanied them, had died or disappeared. Moreover the captain has a servant who is seriously underpaid and treated unfriendly. There are reasons for this, but the crew does not know them, and this is what they see.
PCs have been acting downright mysterious, often going off in order to consult among themselves, or with one NPC.
I am thinking of letting the PCs make a diplomacy check against the ring leader of the possible mutiny at the moment when the next stressful situation occurs, and then roll with the results.
They also have a "mole" in the crew, a person whom they think works for them. However, they do not know this person is an opportunist and will finally choose the winning side. But he might drop some hints as long as he still thinks the PCs are more or less in control of the situation.
I want to introduce the mutiny more to keep the players on their toes than create huge problems for them.