A Blade in the Dark

Background
''Delphine believes that dragons are coming back to life and the next one will resurrect near the town of Kynesgrove. Once I've convinced her that I'm dragonborn by killing the dragon, she promises to explain who she is and what she wants with me.''

Quick walkthrough

 * 1) Talk to Delphine
 * 2) Locate the dragon burial site
 * 3) Kill the Dragon, Sahloknir
 * 4) Return to Delphine

Delphine
Talk to Delphine, she will explain that Dragons are coming back to life. The Dragonborn is then asked to prove that they are indeed Dragonborn by killing a dragon. She believes that the next dragon to come back to life will do so east of the town of Kynesgrove. She will then give the choice to either travel to Kynesgrove together or go there alone.

Sahloknir
Upon reaching Kynesgrove, Alduin will be hovering over the grave. Alduin is performing an act to bring a dragon back to life. Alduin cannot be killed at this time. Once he is finished, the dragon Sahloknir will arise from the grave site. Sahloknir needs to be killed, this will be a tough fight; use ranged attacks when possible, and try to use flank and rear attacks when the dragon lands.

A follower, along with Delphine will be useful for distracting Sahloknir. This fight can be made easier by attacking Sahloknir before he has been fully revived by Alduin. This way his life can be reduced before he's able to fight back. Sahloknir and Alduin are supposed to engage in a lengthy conversation, even addressing the Dragonborn themselves before combat occurs, and rushing in to combat will cause this dialogue to be skipped.

After killing Sahloknir, loot his body. Then talk to Delphine. The Diplomatic Immunity quest will begin, requiring the Dragonborn to go with her back to the Sleeping Giant Inn in Riverwood.

Resurrection dialogue
Alduin: "Sahloknir, ziil gro dovah ulse!" (Sahloknir, I bind your dragon spirit for eternity!) Alduin: ''"Slen tiid vo!" (Flesh Time Undo!)'' Sahloknir: "Alduin, thuri! Boaan tiid vokriiha suleyksejun kruziik?" (Alduin, my lord! The ancient undead rising again?) Alduin: "Geh, Sahloknir, kaali mir." (Yes, Sahloknir, the Allegiance of Champions.) Alduin: "Ful, losei Dovahkiin? Zu'u koraav nid nol dov do hi." (So, you're the Dragonborn? Your voice shines not from Dragonkind, but from yourself) Alduin: "You do not even know our tongue, do you? Such arrogance, to dare take for yourself the name of Dovah." Alduin: "Sahloknir, krii daar joorre." (Sahloknir, slay the mortals)

Trivia

 * If the Dragonborn does not immediately return to the Sleeping Giant Inn with Delphine, then she will wait in the Bannered Mare in Whiterun until they return to Riverwood.
 * The name of this quest may be a reference to the quest A Knife in the Dark from, and a play on those words, or a reference to the eleventh chapter of The Fellowship of the Ring (by JRR Tolkien) "A knife in the dark".

Behind the scenes

 * Unless otherwise stated, the information above was obtained from in-game play or from The Elder Scrolls V: Skyrim Creation Kit.