A lock for a window on a topper cap found on pickup trucks and the like. The lock comprises an inner housing having a rotating geared pinion engaging two racks. The racks are attached to deadbolts that can extend and engage the frame tubing on opposite sides of the pinion gear. An outer housing surrounds the inner housing and the deadbolts. A handle shaft is disposed through the outer and inner housings to attach to the pinion gear. Turning the handle turns retracts or extends the deadbolts. The whole assembly can be easily installed by attaching the outer housing to the window inside surface. The housings make it difficult for intruders to open the window by tampering with the mechanical components.