Ill Met by Moonlight

It is a quest for the Daedric Prince Hircine.

Background
''I've met Sinding, a werewolf who the Daedric Lord Hircine has punished by preventing his transformations. He's given me the ring he stole and asked me to entreat Hircine for forgiveness.''

While in Falkreath, the Dragonborn may hear rumors of the savage murder of a little girl. No one seems quite sure how someone could commit such a horrible crime, but the culprit is currently locked away in the Falkreath Jail if the Dragonborn wants to find out.

The Hunt
Sinding (found in Falkreath Jail, under the Barracks) will tell the Dragonborn of a rare animal, the White Stag, that needs to be killed to appease Hircine, the Daedric Prince of the Hunt. Sinding gives the Dragonborn the Cursed Ring of Hircine, which auto-equips and can't be removed. While worn, it causes the wearer to transform into a Werewolf at random, even if they don't have Lycanthropy. Note that transforming will remove all equipped items, including the ring, so transforming once will solve the problem of unpredictable transformations.

After that, Sinding escapes. To remove the cursed ring, the Dragonborn must track down the White Stag and slay it. Note that the White Stag regenerates health very quickly, so it may be difficult for low-level players to kill it. It also runs away from the player and followers, just like a regular Elk. Sneak-attacks with bows will be useful here, as well as powerful Destruction spells, such as Incinerate and Icy Spear, especially if dual-cast. After having killed it, the Stag's spirit appears and approaches the Dragonborn, and Hircine will speak through it. He commands the Dragonborn to go to the place where Sinding has fled, and to kill him to gain the Daedric Lord's favor.

Sinding can be found at Bloated Man's Grotto. After arriving, the Dragonborn will meet some hunters, who are outmatched by Sinding. Note that if the player is in werewolf form, talking with the necessary characters is not possible, so wait for it to wear off.

Talking with the dying Khajiit will reveal that Sinding is too strong for the Hunters of Hircine, and he will tell the player to kill Sinding in the name of Hircine before dying. The objective at this point is to wander through the walkways until Sinding is met in a clearing; he will speak to the player from his perch on a rock outcropping. There are two choices at the end of the conversation; one is to tell him that he will be killed for Hircine, the other is to tell Sinding that they will kill the hunters for him.

Killing Sinding
Picking the dialogue option to kill Sinding will make him accept his fate, though he will flee through the pathways away from the player, killing Hunters has he goes, until he reaches a dead end.

Sinding is a powerful foe, and often uses power attacks. Frost-based attacks can be useful here, as they will drain his Stamina, preventing as many power attacks. Note that he is immune to paralyzing spells and potions. When low of health, he will not yield but rather attempt to flee. This can be used to an advantage to attack him without reprisal. After he is dead, skin him and the aspect of Hircine appears in Sinding's ghostly human form, congratulating them and gives the player the Savior's Hide.

Saving Sinding
If the dialogue option is selected to spare him, Sinding will be grateful, and he will help the player kill the Hunters, saying "We will hunt together!"

Even if a high level, the Hunters are not very powerful foes; and still wear low-level armor, such as hide, studded, and fur armors. Some Hunters wear only clothing, while one or two wear Steel Armor. Each area along the path to the dead end has two-three Hunters. Having a follower along will help if having trouble, and Sinding can kill the Hunters in two hits.

After the dead end is reached and the Hunters have been killed, speak to Sinding. After the conversation ends, leave him and exit the Grotto to meet Hircine, who will congratulate the player and give them their reward.

Reward
The reward received varies depending on the Dragonborn's choices:
 * 1) If Sinding is killed and his skin taken, Hircine appears and rewards the Dragonborn with the Savior's Hide, a leather-based light armor which gives 15% magic resist and 50% poison resist.
 * 2) If the Dragonborn spares Sinding and kills the hunters, Hircine will appear upon leaving the grotto and commend the Dragonborn for turning the hunt "inside out," giving his blessing and transforming the ring into Hircine's Ring. This ring gives the Dragonborn unlimited werewolf transformations per day, but only if the user is already a werewolf.

It is also possible to obtain both of these rewards using one of a number of similar exploits:
 * Kill all the hunters, speak to Sinding, go outside the grotto and claim the Hircine's Ring, then go back in and kill Sinding to get his skin. The spirit will reappear from Sinding's corpse and offer the Savior's Hide.
 * If the above doesn't work, kill and skin Sinding immediately after killing the hunters and talking to him. As soon as the Hircine spirit appears, back out of the conversation and run out of the grotto where the White Stag spirit will appear and bless the ring to break the curse. Return to the grotto and resume conversation with the Hircine spirit to receive the Savior's Hide.
 * A further way that can work to receive both rewards (if the first method results in not being able to skin Sinding upon return and the second method results in a non-speaking Aspect of Hircine in the grotto upon return) is to kill the hunters, kill Sinding near the exit, complete the conversation quickly to claim the Savior's Hide and then sprint to the exit to claim the Ring outside. It is also possible to achieve this with console commands. If you can't kill Sinding by the entrance, you can simply kill him wherever possible, acquire the Savior's Hide from the Aspect of Hircine, then immediately open the console and enter, and you'll be put at the entrance to Bloated Man's Grotto, where Hircine will bless the ring as per usual.
 * Leave the grotto along with Sinding after killing the hunters.  When the Stag spirit appears, back out of the conversation and kill Sinding, then skin him and speak with the spirit emerging from his corpse for the Savior's Hide. Speak to the Stag spirit again for the ring.
 * A fourth way to obtain both the ring and the hide, if you originally obtained the ring, is to return to the grotto at any time in the game. Upon entering the main area you will see Sinding in werewolf form. Killing this version of Sinding will only result in obtaining ragged trousers. However, if you follow the trail through the grotto, as you did on the original hunt, you will find yourself on a ledge overlooking the main entrance area with a second version of Sinding--one on the ledge with you, and another below. If you kill the second version of Sinding you will receive the option to skin him, causing the Aspect of Hircine to appear and convert the skin into the Savior's Hide.
 * Another way to getting both rewards is to first kill the hunters with Sinding, then drop the ring, then kill Sinding and skin him for the first reward, pick up the ring and leave the cave. Leaving the cave with the ring will trigger Hircine to come and give you the Ring Of Hircine reward while keeping the Savior's Hide.

Trivia

 * "Ill met by moonlight, proud Titania," is the Fairy King Oberon's first line in A Midsummer Night's Dream, a comedy play written by William Shakespeare.
 * There is also a WW2 book with this name, later made in to a film starring Dirk Bogarde.
 * The White Stag is a reference to King Arthur and the Knights of the Round Table. In the legend, the Stag has a perennial ability to evade capture, and the pursuit of the animal represents mankind's spiritual quest.
 * Both quest rewards count toward the Oblivion Walker achievement. Obtaining both makes the achievement obtainable even if another Daedric quest is failed.
 * If Sinding is killed either before or after helping him kill the hunters, he cannot be resurrected via console after he has been skinned. This is because at that point he has been scripted to die.
 * If the Dragonborn is a vampire, they will not be able to transform into a Werewolf because lycanthropy and vampirism are not compatible.
 * If the Dragonborn is a vampire during this quest and chooses to kill Sinding for the Savior's Hide, the hunters fighting him may order "Kill the vampire!" even though the Dragonborn is not the target.
 * If Sinding is spared, he may appear in a random encounter later on. He will be in werewolf form and hostile, fighting a Hold Guard.

Bugs
Зов луны Schicksalstreffen im Mondschein Emboscada nocturna