If you've been a good slave, congratulations. You've shown great potential today, and you have earned a satisfying final orgasm before you are locked up.
While you cum, I want you to beg me to lock you up. I want you to say "Please lock my cock Mistress" three times. Once before you cum, once while you cum, and once after.
Keep the tip of the plug right at the entrance of your ass, and right before you cum, insert it fully. Feel it rub against your prostate as your ass contracts in orgasm.
Do it now. CUM FOR ME!
Oh that gets me so hot!
Go clean yourself off and wait for your cock to go soft. Leave the plug inserted.
And don't be long, I want that cock locked up asap.