Sex und Ex.

When Leo invites his hip and trendy ex-girlfriend to a friendly dinner party, Grace turns to Will, Jack and Karen to round out the guest list and keep the night running smoothly. However, when Leo's ex turns out to be the only girl Will ever slept with, Grace's jealousy gets the better of her. Meanwhile, Karen discovers Lorraine's dog Chompers hiding in Stan's closet and searches for a new owner for the puppy.