Bernice Takes a Plunge — Ann Harth

Bernice Peppercorn's imagination fills her mind and her notebooks with adventure and intrigue. She sees crimes where there are none and races to the local police station daily to fulfil her civic duty.
When a real robbery is committed in town, Bernice dives into detective mode and stumbles across vital clues that could help find the thieves. No one believes her except Ike, a one-legged fisherman who lives down at the wharf.
Bernice Takes a Plunge is an exciting and humorous adventure for middle grade readers.