A pit bull is a Clue hunter's best friend. This pit bull, Arnold, belongs to the Holt family. Eisenhower Holt; his wife, Mary-Todd; and their three kids, Hamilton, Madison, and Reagan, are traveling around the world in search of 39 Clues that lead to great power. The Holts are the strongest Clue-hunting team out there and are as rough and tough as a family of rhinos. But if you manage to get past the Holts . . . well, then, you have to deal with Arnold. Grr.