I removed the handle (improvising a way to access the screws with the door closed...), thinking maybe the lever was somehow broken. The lever is fine and is turning the internal mechanism. However, when moved to the unlocked position, it appears one or both of the hooks remain in place.
I'm not sure how to proceed. I can't get the door open to replace the lock.
To be clear, the lock is the double hook mortised lock. Internal, with three holes accessible when the door is closed.