Searchlight — Ann Bryant

Twelve-year-old twins Zane and Finola, together with their mum, crash-land on Earth from the planet Sevent. The three are following Dad and are desperate for them all to be together again. The twins have to remain hidden to avoid suspicion as they wait for news, but when cryptic messages are received from Dad, they must break cover and venture out into the world to discover their meaning and have a chance of reuniting their family.