Find the source of the Twilight's Hammer in the Vermillion Redoubt and destroy it.
Every inch of air and every hill surrounding the redoubt is constantly under the watchful eye of Lira's drakes. They must have found a way into the shrine from beneath.
Take this Flashgrowth mote. It should prove more than sufficient to close any hole, tunnel, or portal they might have used to get inside our defenses.
Find the breach in our defenses. Close it.