Your brother's wife comes to ask you a favor...a HUGE favor, actually. You can't ever tell him, she makes you swear you won't. She needs you to do something. Well, not much, really. All you'll have to do is lie back, and get hard, and stay that way, until you cum, deep, deep inside her. She swears its the only way she's ever going to get pregnant, what with the troubles they've been having, how averse your brother is to seeking out help...he'll never know the difference! Although, she's quick to point out some key differences between you and your brother. Mainly, the big, huge difference in a certain important metric! She said this would be "totally clinical," but you've never had a medical professional talk about your cock that way--or suck and stroke it that way...or fuck and drain it like she's doing!