The Cellar ( The Cellar #1) by Natasha Preston-New

Nothing ever happens in the town of Long Thorpe – that is, until sixteen-year-old Summer Robinson disappears without a trace. No family or police investigation can track her down. Spending months inside the cellar of her kidnapper with several other girls, Summer learns of Colin’s abusive past, and his thoughts of his victims being his family…his perfect, pure flowers. But flowers can’t survive long cut off from the sun, and time is running out….