The Lost City (Edison Beaker, Creature Seeker, Volume 2)

Edison Beaker and his sister, Tesla, head back through the Night Door and stumble into a mysterious city that's sinking into darkness. He could be a hero and help restore light to the city and its inhabitants who are crushed by gloom. But who can he trust to help him? His old friend, Knox, who is acting a little cagey? A new friend, Smudge, who's a dreaded Underling, but seems pretty helpful And, oh no! Now Baron Umbra is back and wants vengeance!

Edison is about to find out if he has what it takes to be a Creature Seeker.