Okay, so this turned out a little long, and are more plot twists than dilemma's...
I ran a campaign a while back which revolved around a powerful merchant fighting a covert war against a lich (one his ancestors) to protect an ancient artifact which would allow the lich to gain the power of one of three demi gods, thus paving the way for an ancient evil to arise. The fight had been going on for generations, and had thus far cost the lives of the merchants family, including his son, a reckless paladin. Now, this merchant, one of the most powerful in the kingdom, had used virtually all of his wealth fighting this losing battle. Forced to desperate measures, he blackmailed and coerced the party to undertake some suicidal tasks for him (crossing a vast desert by an unused route for example). The PC's of course, knew none of this, and just though him a manipulative bastard.
Anyhow, evetually the thief in the party (a member of the local 402: thieves, assassins, prostitutes, conmen and beggars) decided to take matters into his own hands. Hiring a friend of his, he sent him out to dig up some dirt on the merchant. Needless to say, the friend returned, badly beaten, suggesting that the next time he needed a favour, to ask somebody else and that maybe he'd check out the opportunities in another country for a little while. This worried the PC thief, but not nearly as much as waking up with a dagger against his throat that night, held by what the pc's though was the merchants chief administrator (in actual fact, a front runner for the head of the thieves guild 20 years ago before the lich's agents seized control, and he was forced to fake his own death).
Quote, next morning at breakfast: "Um, I think Gregor's a little more than an ordinary merchant, and we'd better be nicer to William (the NPC 'administrator').
In the same campaign, the cleric was being played by a newbie to D&D, and I decided, since she didn't seem to be enjoying the combat aspect as much as the others, to throw some RPing her direction, by introducing a love interest at one of the merchant's parties. The NPC in question, a charming, handsome, wealthy and urbane member of the old aristocracy (the country was now run by merchant princes and a consortium of other guilds). Not to let a good plot hook go by unmolested, I made the NPC a vampire spawn, a low-mid level servant of the lich. The backstory being that she reminded him of an ancient love and part of the reason he became a vampire (he was waiting for her to return). He courted her over the course of probably 5 sessions+, whenever she was in the capital. I had decided that the vampire was capable of redemption but the player, unbeknownst to me, had decided to develop a relationship with one of the other PC's and told the vampire this. The ensuing kidnapping and battle were epic, probably the best in the campaign. The PC's were a little concerned when they broke into his mansion, and found a room filled with hundreds of pictures of a woman that looked almost exactly like the cleric, wearing gowns hundreds years out of date.
Best quote (by the thief PC upon realizing the cleric hasn't returned, and discovering the body of another investigator they hired to check out the Vampire's background): Um, so has anybody seen Kail in the daylight?