The Undertaker's Gone Bananas — Paul Zindel

Bobby Perkins knew the minute he saw Mr. Hulka, his sinister new neighbor, that the man was evil. Then one morning, while spying on the man, who works as an undertaker, Bobby thinks he witnesses a violent crime. Bobby is determined to expose Mr. Hulka, and he asks his best friend, Lauri, to help him. The two sleuths discover much more than they bargained for. Can Bobby and Lauri stop the evil Hulka before he claims his next victims?