Here are five trucks with a single purpose. Clue #1: A boy and his father watch the busy drivers of the five trucks through a large window. Clue #2: A plaid suitcase is an important part of the progress that father and son are following. The five trucks -- each labeled appropriately as catering truck, baggage tractor, baggage conveyor, mechanic's truck, and push-out tractor -- all belong to a team. And their focus? One airplane, which viewers gradually see in greater and greater detail as takeoff nears. The text is brisk, the watercolor illustrations meticulous yet breezy. At the end, the airborne boy waves through his plane window at the five drivers who have become -- for him and for this appealing book's young audience -- as good as friends.