The final exciting instalment in the Miss Penny Dreadful series from acclaimed author Allison Rushby. Searching for a new story idea for her aunt's famous penny dreadfuls, Penny and Aunt Harriet decide to follow up a newspaper article about a mysterious mermaid's grotto. Hidden down a secret passageway on the banks of the River Thames, the only way to enter is through a tavern, aptly named The Mermaid's Locks. In the glittering grotto, Penny and her aunt find a comb with some strands of the mermaid's red-gold hair. Penny sets out to investigate - can the mermaid truly be real? Also, why doesn't Mr Crowley, Aunt Harriet's publisher, want her to write about it? Meanwhile, another cryptic postcard arrives from Penny's missing parents. Nothing is as it seems in Penny's world. Will Penny be able to finally piece together all the clues?