One shot in (one's) locker old-fashioned noun phrase
One shot in (one's) locker is the last opportunity for someone to successfully achieve something.
This game is one shot in our locker, so try our best to reverse the situation.
Tonight he will fight as if it's the one shot in his locker.
Nothing but fortunate chance
If you take a flyer (on something), you take a chance, risk, or gamble on it.
Having only one chance left one can do in order to achieve something
A second opportunity
Very little chance of succeeding in doing something
Locker is a drawer, cupboard, or compartment usually seen at gymnasiums, schools that may be closed with a lock. Bullets/ammunition might be stored in it in this case (the word "shot"). Maybe that's why we have this idiomatic expression.
To be very wet
Because of forgetting bringing an umbrella, I look like a drowned rat when it rains.