Twelve year old Maisie’s grandmother owns a boarding house in Victorian London.  Maisie helps clean and views herself as an amateur detective.  In this 4th book of her adventures, a rare, feathered mask has disappeared from the collection of tenant Professor Tobin.  As Maisie begins to piece together clues, the astute reader can also identify the likely thief.  An interesting twist at the end tells why the mask is so valued.  These mystery stories contain enough twists and turns to captivate budding detectives and problem solvers.  These books do not need to be read in order.