She's your best friend, your worst enemy and the one person you can't live without!

Flirty, flaky party girl Maggie (Diaz) and plain, dependable lawyer Rose (Collette) are sisters, best friends and bitter rivals who seem to have only two things in common: DNA and the same shoe size. Only when their love-hate relationship veers toward the hate end of the spectrum - do they accidentally discover they also share a long-lost grandmother (MacLaine), who enriches their lives and helps them make peace with each other - and themselves!