Ages range 8 - 12 years. Holiday house First published in 1955 as Holiday house. Updated and altered to become part of the Riddles series in 1997 by Enid Blyton's daughter Gillian Baverstock. Summary : Katie and Nick are excited to spend their summer at Holiday House with its kind owner Mrs Holly, her bossy daughter Clare and the mysterious Gloomy Gareth. But while exploring the beach and the surrounding cliffs they discover a secret network of caves and an abandoned house. But who is hiding there, and what are they hiding from?