Nina and her parents are having an adventurous holiday, deep underground in a cave. But Nina gets separated from the tour group and is suddenly alone in the dark. With the help of the light of thousands of glowworms, she is able to find her way to safety. Sapphire level titles provide a selection of stories and non-fiction titles chosen for their range of content, narrative and points of view. This level encourages readers to form opinions and discuss their own reading tastes. PM Plus Chapter Books (levels 25–30) provide a selection of stories chosen for their broad range of content, characters, topics and points of view. The high-interest topics include adventure, emergencies, natural disasters, risk-taking, historical events and investigation. #pm19-offer