Anyone for a Threesome?

After getting tipped off, Melanie goes home and catches Sarah in her bath, wearing her bath cap, clearly having an affair with her husband. While considering her reaction, she can't help but become aroused by the luscious Sarah. After all, she and her husband Marcus have often discussed how much they'd like to experience a threesome.

When Marcus suggests another threesome, Melanie is quick to agree. But she's expecting Sarah, not Marcus's best friend John, waiting to join in.

What can a girl but go with it?