Broken latch

Hello, thank you for posting,

Please start by reviewing the 82-218 mortise lock to see how the dimensions compare to your original. Also review the installation videos on the page. 

I also recommend checking the thumb lever on the handle set itself to make sure there is no damage to confirm the route cause of the problem. If the the lever is in good shape, you can insert a slotted screw driver into the mortise lock keyway to try to throw it. If it is not moving, the mortise lock is the issue. 

Please review and let us know if you have any additional questions!