A little boy's daily "Knock Knock" ritual with his father-pretending to be asleep when Papa knocks before throwing himself into his father's arms and being told "I love you"-comes to a sudden and inexplicable end on a morning when the knocking never comes. Papa's not there to help the boy get ready for school, or cook him eggs, or help with homework. Days turn to months. Eventually a letter comes from his father, offering advice for the present and future: "Knock Knock down the doors that I could not. Knock Knock to open new doors to your dreams ... Knock Knock with the knowledge that you are my son and you have a bright, beautiful future. For despite my absence, you are still here." The lack of explanation regarding where the father has gone is both unsettling-as it should be-and powerful. It enables many children who are dealing with absence or loss to put themselves into this moving, affirming story. Bryan Collier's illustrations show an African American child who is clearly loved by both an absent father and a very present mother. In an author's note, Daniel Beaty shares how his father was his primary caregiver when he was a small child, then was incarcerated. After one upsetting visit, Beaty didn't see him for many years. (Ages 4-9)