Instructions
Visit the Emporium and talk to Casey. He tells you that he no longer has Horace's Book.
Walk into the Ice Cream Parlor and talk to Paulie. Paulie gives you the book. Return the book to Horace's Detective Parlor.
Pay a visit to Casey and talk to him again. He asks you to return his missing key and explains that he lost it near the Ice Cream Parlor.
Walk toward the ice cream parlor. Enter the alley, located just before the Ice Cream Parlor, and walk toward the manhole cover at the end of the alley.
Equip your paint thinner and use it on the manhole cover. Wait for the paint thinner to dissolve the manhole cover.
Jump into the hole and pick up the nearby key.
Return the key to Casey to earn a power spark.