The House of Secrets — Jean Davidson

When orphan Laura Crestwood overhears her relatives planning to marry her off to a much older man, she secretly takes the job of secretary as far from London as she can, in rural Devon. Brendan Colefax is young and attractive, and Laura enjoys her work helping him with his scientific experiments, although he will not reveal their purpose. The nearby village of Manleigh relies on farming, but when animals fall sick Brendan is blamed, and his laboratory set on fire, although the work carries on, with Laura growing increasingly fond of him. Then Laura is knocked from her bicycle and kidnapped...but who is to blame and why?