There are three things to know about Tilly Mahoney:

1. She's a liar.

2. She thinks she's in love with her best friend.

3. She's got a plan to ruin his wedding.

Tilly and her best friend have been through it all. For decades, he has been her support system, and she's been his right hand gal, and now he's engaged to someone else? Not on her watch.

"Hey, want to help me break up a wedding?" is a dubious start to an unlikely friendship, but the bride's ex-boyfriend, Zack, is the perfect partner in crime for Tilly's misguided plan to spoil the nuptials. The bearded and brooding man is clearly desperate to win back the love of his life, and she's all too willing to help if it'll break up the happy couple.

But the more she tries to interfere with the wedding and the closer she gets to Zack, the more confusing Tilly's feelings become. About a decades-long friendship, about what she thought was love, and most terrifyingly, about the way Zack saves all of his smiles for her.