Rescue

 is a repeatable quest offered by Florentius Baenius in Fort Dawnguard. To complete it, rescue a friend or spouse from a Master Vampire in a randomly selected location across Skyrim. The friend in question is anyone that has a friendly disposition towards the player no matter who it is. It's even possible for the kidnapped friend to be a Jarl.

Players should be careful when doing this quest; sometimes, when rescuing the Dragonborn's friend, the friend will be killed by the Master Vampire. The quest objective will remain, saying to rescue the friend, but clicking to search the friend's corpse still completes the objective. Returning to Florentius will result in him congratulating you on your successful rescue, even though you technically failed.

Bugs

 * Sometimes, if the victim is your spouse, they may remain at your home instead of appearing at the cave, therefore messing up the quest. If this occurs, load an autosave. This may fix it and get a new victim.
 * Sometimes the marker for the quest points you in random directions.
 * Occasionally, speaking to your spouse after rescuing them will start a new Rescue quest; leading you to a new vampire to kill. However, the vampire doesn't actually spawn in the area - leaving the quest unfinishable, and thus unable to get any more quests from Florentius Baenius.
 * Sometimes the victim will not be gaurded by the vampire instead they reside in thier usual place. This does not affect the quest but the player will still have to 'rescue' them even though they are technically not captured.