A likely story
Definition 1 of 1
Pro Tip 1/3Skepticism Expressed
Use when you doubt someone's story or find it hard to believe. 
He said he caught a fish this big? A likely story!
Pro Tip 2/3Sarcasm Detected
Often carries a tone of sarcasm or irony. 
Sure, you finished all your homework in one hour. A likely story!
Pro Tip 3/3Informal Usage
Mostly used in informal settings like conversations among friends. 
You just forgot to call me back again? A likely story!