This plot is meant as a strategy exercise to give a change of pace for high- status characters (ie the characters are recognised and respected).
The idea may be of use at a lower level. Characters with scrying and/or night vision capacities will be especially useful.
Plot. A coastal region about a port town has become the target for foraging pirates, based somewhere in a nearby archipelago. The lord in the town has asked the characters to assist in setting up a defence against this menace. Mostly the raids have been strictly foraging but a recent one overpowered a sleeping manor, killing its owner and with all the young women carried off. For groups so inclined this plot can easily include a simple board game based on the map, with the turn being a week, and then dicing for if and where an attack will come. The GM then looks at what the characters have put in place and adjudicates a result. The GM can control events on a more abstract level if this doesn't appeal - the fun is in devising the strategy and counter-strategies. They should be thinking up plans for watches, message passing, deployment of forces etc. A good place for the characters to get directly involved is in attacking the boats themselves while the bulk of the crew are raiding inland.
Here is a more detailed scenario as an example.
The Pirates. These are actually the losing navy from fratricidal wars on the far continent preying mostly on their own countrymen's merchant trade in vengeance. They have 12 viking-style boats with crews of 20-40 each. The leader is a cunning captain and will order appropriate measures against defences (ie, they will understand a lit beacon and its implications as well as the intended receivers). The coastal strip concerned is very convenient and it would be difficult to go further afield. It is only due to a botched campaign against them that they are forced to forage off the coast to this extent and the word is forage as opposed to rape and pillage. The leader did not order the attack on the manor and was not amused when he found out about it, guessing correctly that it would result in stronger defences. The usual attack mode is to travel well off-shore (though they have been slack so far) at day, then run ashore pre- dawn. The raiding party goes inland while 5-9 remain to guard the ship, usually lying slightly off-shore rather than beached. The raiding party will be competent fighters though they will back off from significant resistance, particularly if it endangers the ship. Animals are driven back to the ship on the hoof, while anything else has to be carried on the raiders' backs. If a ship does not return or has encountered major opposition, then further raids will remain well out of sight of land by day. If a second ship is lost, then the raids will be carried out by two ships at a time to make a large combined force with extra guards on the ship. The loss of four ships will force the captain to move foraging elsewhere and raids will cease.
Resources. The town lord has a sizeable following of men-at-arms based in the castle as well as three fighting ships, properly part of the navy. These ships will outpace the pirates on short hauls, (less than 1 hour apart), due to superior no.s of oarsmen but are no match for the longboat under sail as the oarsmen tire. There are 20 villages/hamlets scattered about the coast that can raise ill-trained militia at a push (ie with a backbone of real men-at-arms in command) but mostly the villagers will be too concerned with protecting family as they hightail out of it, probably driving herds if they have time. There will be one or two manors of nobles near each village though and these usually retain 2-6 men-at-arms who can be commanded. The population will be generally enthusiastic for measures to counter the pirates, particularly if they don't have to actually do the fighting. They will man look-outs and beacons reliably.
Any time a pirate is captured, there is a 50% probability of finding a chart (providing the ship isn't fired). This covers the coast and archipelago quite well and while it wont locate the pirate base, it will be noticeable that part of the archipelago is drawn in far more detail than the rest.