The Gift

It is a quest that can be obtained from Vingalmo in Castle Volkihar. The Dragonborn is required to turn his/her spouse into a vampire.

Walkthrough
To begin the quest, the Dragonborn needs to first be married. Next talk to Vingalmo and he will initiate the quest. Additional side quests given by the vampires of Castle Volkihar need to be completed before Vingalmo will initiate this quest. The Bond of Matrimony is not required to be worn and is also not required to be in the Dragonborn's inventory.

In order to turn a spouse into a vampire, first use Vampire's Seduction to calm them, then feed on him/her.

Trivia

 * It is not possible to turn Aela the Huntress, Farkas, or Vilkas into vampires, as they are already werewolves. However Vilkas and Farkas can be turned if they're cured from their lycanthropy. Any other member of the Companions or anyone else is turnable.
 * In some cases, spouses turned into vampires by this quest will not gain the same type of glowing orange eye that all vampires do. Some characters, like Ysolda, will have very dark red marks below her eyes, instead of her normal bright red.

Quotes

 * "I never knew the darkness held such colors, or the night air smelled so sweet. You have given me a great gift." - First comment made by spouse after becoming a vampire. Also said by the target of the New Allegiances quest.

Bugs

 * If you are married to Erik the Slayer and bite him in a location where he can't get to a bed or coffin before the Vampire's Seduction wears off, Erik is likely to turn hostile and attack you.
 * This may be avoided by biting him near your home's bed.
 * Despite being turned into a vampire, spouses may be highlighted in Detect Life spell instead of Detect Dead.
 * For unknown reasons, it is possible that Vingalmo will not give the quest.

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