Unlock a doggy door

The kennel was empty. Dry dog food lay untouched in the metal trough. The big water can was full to the brim. There was no sign of any
disturbance.

At the far end of the kennel was the ingenious dog door. It led to a narrow ramp that rose to the surface. Clark used it to take the dogs outside when it was time to exercise them, so he wouldn't have to run them through a camp hallway. Wind whistled along the door's edges.

Clark and Garry examined the latch, which normally held the door shut. It was carefully designed so that no dog could accidentally open it.

"It's not broken?" The station manager spoke quietly as he fingered the insulated backing of the metal.

"It's not." Clark tapped the latch. "This was wide open when I came in this morning. I know I latched it. I always check it before going to bed."