The Trouble with Goats and Sheep by Joanna Cannon

Summer, 1976
 
Mrs Creasy is missing and The Avenue is alive with whispers. As the summer shimmers endlessly on, ten-year-olds Grace and Tilly decide to take matters into their own hands. But as doors and mouths begin to open and the cul-de-sac starts giving up its secrets, the amateur detectives will find more than they could have imagined…