Adventure in the Haunted House (Vintage Paperback) by Page McBrier

Dogs. Snakes. Gerbils. Ducks.

Animals are Oliver Moffitt's business, and there is no pet-care job he can't handle. So it should be no problem for him to take care of Princess Fluffy, a friend's pampered cat.
Unfortunately, the life of a pet-care expert is never so simple. It's bad enough when Princess Fluffy gets loose and disappears inside a spooky, boarded-up house. But when Oliver hears a ghostly sound from inside the "empty" house, he calls on his friends to help him find the missing cat. And that's when the funny-and scary-adventures really begin!