The Weight of Silence by Heather Gudenkauf

“Two little girls are missing. Both are seven years old and have been missing for at least sixteen hours.” Calli Clark is a dreamer. A sweet, gentle girl, Callie suffers from selective mutism, brought on by a tragedy she experienced as a toddler. Her mother Antonia tries her best
to help, but is trapped in a marriage to a violent husband. Petra Gregory is Calli’s best friend, her soul mate and her voice. But neither Petra nor Calli have been heard
from since their disappearance was discovered. Now Calli and Petra’s families are bound by the question of what has happened to their children. As support turns to suspicion, it seems the answers lie trapped in the silence of unspoken secrets.