More than one way to kill a cat

"well, thought harry, did you want to hear my list? a snail plague, an unsolicited pet, a missing client, a missing spade, noises in the dark, a whole nest of dead cat and kittens, and - did i mention it? - another missing client! talk about being over it." harry is a gardener, who occasionally has to kill things for a living - weeds, insects, snails. this makes him a murderer, according to his five-year old daughter martha. she wants a snail for a pet, before he "petticides" it. but a cat will also do. on the same day that martha's pet arrives, harry discovers something buried in a client's garden. but then the client disappears. while harry is confronted with deaths and disappearances, his wife nancy goes on a wild goose chase searching for the meaning behind the find. harry learns there is no easy answer to the question: when is killing murder?