[1] A model predicts that a planet will cross its star every twelve days. [2] The first four observed crossings fit that schedule. [3] The fifth crossing occurs noticeably late. [4] The gravity of a second, unseen planet could produce such timing variations. [5] A revised model containing a second planet predicts that the next crossing will also be delayed. [6] The next observed crossing matches that prediction. [7] The system probably contains another planet rather than merely an irregular orbit for the known planet.