Murder Must Wait - Arthur W. Upfield

In the little town of Mitford, New South Wales, four babies have been stolen - all boys, all under three months old, and all apparently neglected by their mothers. The local police have given up and the trail is cold. Then a fifth child vanishes, and the mother is found dead next to the empty cot. Inspector Bonaparte is called in, first to find the missing children, and only then to solve the murder...

Bony - a unique figure among top-flight detectives. - BBC