The Rational Man is a quest assigned by Al Martin. Al is concerned about his friend Jim Gallager because he is keeping an infected locked up. He asks Joe if he'll please go check up on him. Upon entering Gallager's Gulch Joe discovers that it's true that Al has been keeping an infected. Jim tells Joe that her name is Cassie Short and she's a special infected that can talk. Joe is skeptical and tries to convince him that it's a bad idea to keep her, but he fails convince Jim.
To complete this quest you must have Alice Ivers talk to him. Alice is able to convince Jim that he should put Cassie out of her missery. Jim asks Alice to do it for him, Alice obliges and just before shooting Cassie she speaks to Alice: "I know who you are!".
After the deed is done return to Al for a 50g reward.