Mase Stirling—with his balls and his billions—might be the perfect leading man for some. Not Fiona. Mase is a baseball player, billionaire’s son, and all-around fun guy. He collects names and numbers as easily as his father pays the bills, sliding into DMs as smoothly as he slides out of their lives. He's a player both on and off the field and all the tabloids stories prove that he likes it that way. Fiona prefers the quiet life, happy to watch her friends fall in love like one of her favorite romance novels. Mase, with his leading man looks, isn't the type to be a knight-in-shining-armor—at least not until he swoops in to rescue Fiona from a panic attack in the middle of a Las Vegas nightclub, But after a few Alabama Slammers, some dance moves even better than Sam Rockwell, and her own Pretty Woman shopping spree, Fiona realizes there's another side to the scoundrel Mase Stirling. A side she might actually be falling for. But when family and furious ex-girlfriends get involved, Fiona's happily ever after is threatened. Will Mase be able to rescue her again, or will she have to save herself? Marrying the Billionaire Best Friend is the fourth book in the Suitor Science Series, a sweet romantic comedy with a billionaire bad boy and the sweet, shy girl next door proving that opposites do attract, and true love might be found in Las Vegas.