put key in it slide the lock back in the hole open case and re attach the latch .. it looks like the latch came off " usually will have lock tight on the threads or a lock washer" Use both when re installing.
I found a plastic tab underneath the lock and under the handle. It looked like it was a plastic latch - but it wasn't. It eventually broke off and exposed a hole under the lock. After about 20 minutes fiddling around with a screwdriver not knowing what I was doing I eventually got lucky and popped the latch.
Now the whole lock mechanism, latches, nut, washer, and cover are all in pieces and I'm pretty confident I can figure out how to put it all back together. I'll document the whole thing with pics because I'm sure this is going to happen to someone else some day.