A shot in the locker old-fashioned noun phrase
Having only one chance left one can do in order to achieve something
This is a shot in the locker. I can't screw it up.
It's very intense right now! Peter has a shot in the locker.
Don't lose hope! You still have a shot in the locker before everything goes south.
The last opportunity for one to achieve something
If you fall for someone's trick the first time then they are at fault.
Are you going to mess with me again? Fool me once, shame on you; fool me twice, shame on me.