back to base while clearing the keep's first level, they run into one of Keep on the Shadowfell's interlude encounters, entitled The Dead Walk.
The encounter starts with returning PCs discovering Winterhaven's gates securely locked. When they question the town guards, they learn that undead have been sighted in the village graveyard to the south, and despite the village having a 20-something strong militia, a barracks, a siege supplies warehouse, a reasonably competent local wizard and a Fighter's Guild, the town have decided to stick their heads in the sand and wait for the players to come and save them.
When the players bow to the inevitable "fight some undead in a graveyard" cliche, and head down to the cemetery to check things out, they find to nobody's particular surprise that the shambling skeletons in question are headed by Ninaran The Obvious Spy.
The Dead Walk takes place on another of Keep's legacy maps, recycled from an earlier Dungeons and Dragons product, which explains the odd setup. There's a large tomb in the west with some suspicious coffins, which has absolutely nothing to do with the encounter, and there's another of the glowing magical circles which Keep is so fond of. This time around the circle is described as powering the necromantic ritual which keeps all the skeletons fighting, and enterprising players can break the circle with some Religion or Arcana skill checks to bring a swift end to the encounter.
It's a stupid set-up, plot-wise. Having the skeletons milling aimlessly in the graveyard is as far from dynamic as you can imagine; there's not even any time pressure in the module as written - it's assumed the undead will stand around until the players get around to killing them. A more interesting scenario would have seen the undead assaulting the town directly, with players scrambling to save hapless NPCs from the ravening horde. Indeed, several of the Keep conversions floating around the internet make this precise change.
Also, it's unclear exactly what Ninaran is up to. A note found on Ninaran's body, when defeated, suggests this was a plan to kill off the players to stop them meddling in Kalarel's plans. Indeed, Ninaran, like almost every other enemy in the adventure, sets an ambush, having her skeletons burst from the ground once the adventurers reach the centre of the graveyard. It's not a particularly great plan, seeing as the players have already been told that the graveyard is full of undead, but at least she tries.
It's a pretty crappy attempt, though. She could have led her undead to the keep to reinforce Kalarel, or attacked the players while they were sleeping at the inn; you get the feeling that the only reason things play out as they do is because the developers had a "graveyard" map that they wanted to get some use out of.
Plot-related gripes aside, the encounter is tactically interesting. The players enter the graveyard from the gate in the northeast. The defender-type characters will probably proceed first, thus triggering the skeleton ambush and getting swarmed with undead minions. At this stage, arcane and divine characters are likely to make a bee-line for the magic circle, correctly guessing that it has something to do with what's going on.
I've seen this happen personally in two games, and write-ups online suggest that this kind of party split occurs fairly reliably. It's great, because the minions are fluff, dispatched in only a couple of rounds, and the real threat is the pair of Gravehounds waiting by the circle. As soon as the squishy undefended caster-types get near their destination, the Gravehounds strike, deploying a nasty bite attack that deals ongoing damage and knocks its target prone. Without defender support, it's likely the casters will spend most of the battle rolling around on the ground trying to keep the zombie wolves away from their throats. It's a sharp wake-up call to a party that may have grown complacent killing goblins, and it's a quick reminder of the importance of working as a team.
The low point of the battle, though, is Ninaran. Despite a reasonably meaty bow attack, she's poorly armoured and doesn't pack a lot of hit points. In the end result, she's less threatening than either Balgron or Irontooth. After what for Keep on the Shadowfell is a relatively long build-up to her big moment, she goes down in moments once any of the party's strikers get her in their sights.