Trap

 "You mentioned you could track it?" asked the old man. 

"Yes, I can locate the main shadow," I replied. "And where is it now, I guess it's hiding among its many brethren outside…"

 "No, it's with us in the palace," I replied. The old man frowned. 

"It was only able to enter after altering the formation around the city and the palace. And since the rest of the shadows are senseless beasts they couldn't replicate it. But now, it can't leave since it needs to re-alter the formation again, and the moment it touches the formation it will be caught."

 "Then we'll just have to wait until it touches the formation…" 

"I don't have time for that. That thing had waited for millions of years, if it wanted to hide and wait, we have no guarantee we'll even catch it," I said. 

"So, junior brother, what do you suppose we should do? Do we split up and look for it separately?" he asked. 

"That's the worst idea I've heard in a while," I said.