Free the Shriek is a side quest in The Darkspawn Chronicles DLC for Dragon Age: Origins. It occurs during the main quest Assault on the Palaces. A shriek attempted to enter the Palace District via the sewer, and it is now trapped behind the sewer gate. Use the ogre to free it.
This quest triggers when you are near the entrance to Fort Drakon on the southern side of the map. The shriek can be found behind a large gate that blocks the sewer on the south side of the district (marked "Sewer Entrance" on the map). Use the ogre's Hurl to break down the gate and free the shriek.