U2 Danger @ Dunwater picks up where U1 left off, riffing on the presence of lizardmen on the smuggler's ship. It turns out that the lizardmen [Aside: are lizardmen actually amphibians?] were striking a deal with the smugglers to buy bulk armaments at a discount. The Saltmartians--concerned that the mud-wallowing lizard-freaks are planning an invasion of their despicable burg--hire/coerce the PCs into running off and dealing with the problem for them.
Reviews of U2 (the D&D module, not the high altitude spy plane) praise this module for "not being what it appears," which is too bad, because what it appears to be is a lizard-themed dungeon crawl, and who doesn't like hackin' up lizardmen? But it turns out that you're supposed to be helping the lizardmen, not flaying them alive. As written though, the party probably isn't gonna figure that out until it's way too late.
Essentially, this module is supposed to put the PCs in a moral quandary when they find out that the the heavily armed lizardmen they've been slaughtering all evening are not planning on harvesting the gizzards of the good citizens of Saltmarsh. Yet the only indication that something unusual is up with these slithery goons is the presence of some Mermaids and other assorted aquatic types sipping tea and snarfing seaweed crumpets in their lizardy den.
Now, if you enter through the front door you'll find this out right away. But the front door involves swimming, so you're probably not going to opt for that one, preferring one of the land-bound entries. Which means that by the time you get to Neptune's tea party, you've already made a stylish belt--with matching boots and luggage--out of the wives, children, and siblings of the lizardude chief and his elite guardsmen.
Fortunately, the Lizardians aren't too sentimental: they'll forgive and forget as long as the party goes off on a wild crocodile hunt on their behalf. Though, since the PCs are working as independent contractors for the Village of NaClmarsh, they would be entirely within their rights to point out to the Lizardmen that this is not within the scope of their agreement and will first require negotiating for additional services with the town council.
But what if a group of PCs actually did take the time to figure out what the Lizardudes were up to instead of collecting their spleens first and asking questions later? Would this module hold up if it was confronted with such thoughtful PCs? Consider this scenario:
Party [approaching the front gate of the Lizardarian Lair]: "All right you slimy, fork-tongued bastards, we know you've been stockpiling weapons for a raid on the village of Saltmarsh. You'd better cut that crap out right now or you're gonna' be in big trouble."
Lizardudes: "Get lost ya' dandruff-ridden landlubbers, we've got a sahuagin invasion to deal with."
Party: "Say who again?"
Lizardudes: "Sahuagins. Evil, scaly bastards? Page 84 of the Monster Manual? Anyway, they've been harassing us for months, moving in on our turf. We're here negotiating with the Locathah and merdudes to team up against those creeps."
[As confirmation, Merdude chief and Locathah chief pop their heads out, smile, and wave]Party [taken aback]: "Oh! So you're not hoarding weapons in order to raid Saltmarsh?"
Lizardudes: "Raid Saltmarsh? Why would we do that?"
Party: "You're certain? No assaulting the village? No rending townspeople limb from limb?"
Lizardudes [somewhat miffed]: "Absolutely not."
Party [crestfallen]: "Very well. Sorry for bothering you."
[Party dejectedly turns to leave. The Lizardudes, their annoyance turned to pity, confer with Merdude and Locathah. After some whispered debate, they turn back to the party.]Lizardudes: "Say, you guys wouldn't want to help us, would you?"
And so, unless the Master of Dungeons has U3 The Final Countdown on hand and prepped for play, your big Friday night gaming session is over before the pizza's even arrived.