On the back of this book it says:

Abel is an elevator boy in Knott's department store. In his elevator there is a mysterious button. When he presses it, something terrible happens. The elevator shoots up - right through the roof - and flies off through the sky with all its passengers. This is the start of a wonderful adventure for Abel, his friend Laura, Mr. Tump and Miss Clatterhoon. They travel the world, see New York, and get mixed up in a revolution in Perugona... They have the time of their lives. In A for Abel the four travelers meet up again and immediately get into new trouble. Poor Laura disappears: after Professor Pinsky's vanishing act she simply fails to reappear. Her friends set off in search of her. They go by wagon, so there's no telling what might happen next!