"Go Fetch" was the ninth story mission in Infamous: Second Son.
While standing on the roof of the building, drop down to the protestors below. You can either disrupt them or leave them alone. Anyways, dash your way up to Olaf's sign above. Position yourself by some boxes and wait for Fetch.
Upon finding her, she'll be startled and run away fast. Hold down 'Circle' to follow her. You'll have to re-press the button every now and then to keep running. Fetch will lead you all across several rooftops, so make sure you stay close. She will eventually lead you to an abandoned theater.
Run up the wall to reach the roof of the theater, and you'll be inside. Here, you must drain out all of the neon signs in the area to weaken Fetch. Once all signs are drained, shoot neon blasts at her using R2 until her health meter is depleted. At this point, after a brief cutscene, you'll be presented with a karmic choice, in which you can either choose to redeem Fetch (for Good karma), or corrupt her (for Evil karma). Once you make your decision, the mission is finished.