The mystery is one that is easier for the animals to solve, since they are able to observe the world from a different vantage point than humans. It's fun to see how Homer and Lulu try to communicate with their humans through newspaper clippings and the squawking of seemingly random words! The perpetrator something of a shock, and young readers should be warned against climbing into sewers, no matter how important their quest.
Cole's pencil illustrations are the real draw here, and will appeal to fans of Garth Williams' or Brian Selznick's illustrative style. Sadly, there are no mice, like in A Nest for Celeste; I have a soft spot for pictures of mice, and some certainly could have been worked into the park scenes!
This reminded me a bit of Eve Titus' Basil of Baker Street, one of my favorites from my childhood, and joins the ranks of books with animal detectives, such as Hale's Chet Gecko mysteries, Gardner's Horace and Bunwinkle and Quinn's Birdie and Bowser or Queenie and Arthur books.