Physics professor Jacob Hicks is an innocent bystander, but that doesn't keep him from once again getting in the middle of a mystery when an unobtrusive shop owner is murdered. When Jacob's imminent breakthrough on his crime-solving computer turns out to be a bust, his sidekick, Emily Dawson, thinks some amateur sleuthing might be a good distraction.

Meanwhile, Paddy the Rat and his cousin Vinnie hope for a quiet holiday in the sewers under Woolaston Road, visiting Vinnie's family. But when a two-legged dumps a bag of jewellery down a manhole, and Vinnie's acquisitive cousin claims it, it doesn't take long for the Rat Mafia to get wind of the treasure trove and make plans for a jewel heist of their own.

But something is rotten in the sewers of Woolaston Road. A horrible sewer smell is spreading along Woolaston Road and into the shops. While fending off a nosey newcomer, dealing with a baffling string of seemingly unimportant burglaries and running from the Mob, how can Jacob and Paddy get out of this stinky mess before everything blows up in their faces?