Penguin movie is just a modified version of the book 'Silent Child' by Sarah A Denzil. Overall storyline is the same, they just changed some details and added a few extra things. Also some parts are exactly same as in the book. For eg, there is a pregnant wife, first son missing and found a few years later, who has behaviour issues and who is not talking, there is an ex-partner, even the description about the child's condition by the doctor is same (about chained ankles and dislike to touch), and finally who the kidnapper is.. Just that climax is a little different. And there are some native changes done to the story. In simple words, movie started with so much build up and expectations but ended pathetically.