This is the second book in the 44 Tiny Secrets series. However, I managed to read and enjoy the entire book without having read the first. From what I can understand, the first book provides the insight as to how and why Betsy acquired 44 mice, but the second book is perfectly fine to read as a standalone novel. One of the details I really loved was how there are 44 mice, so that each have 2 keys each on a piano. The mice are all named after the keys they are allocated to, for example ‘F-to-F Sharp’.