Hermes was the god of many things. Travelers. Commerce. Messengers. Thieves. So as far as the whole morals thing went, he didn't have any formal boundaries.
But he drew the line at child murdering.
Whatever it was his father was afraid this child would do, it couldn't be worth killing her for. Not only did he feel that it was wrong to kill this child, whom he watched play and laugh and hug her parents during his reconnaissance, but it was known that the Fates were often cruel to child murderers. What Zeus intended to do could have negative repercussions for them all.
What could he do, though?
I ssssay you do nothing. It'sss none of our busssiness, and I don't want to get in trouble with Zeusss. He'sss ssssscary.
Oh, ssshut up, George, chimed Martha, snipping at the other snake that wound its way around Hermes' caduceus. We can't jussst let the little girl die. Did you sssssee her collection of sssstuffed animalsss? Sshe likesss sssssnakes! And besssides, we won't get in trouble. Only Hermesss will.
Collateral damage, Martha! George shot back.
"Can both of you just be quiet for a moment?" Hermes griped. He was sitting on the roof of the house across from where the young Sally Jackson lived with her parents. They were supposed to leave for their flight in less than twelve hours.
Fine, said Martha. Take it out on the ssssnakess.
"Wait." Hermes snapped. "That's it."
The plan was simple. Martha would slip into Sally's bedroom through her window while she napped -- Why Martha? George had asked. "Because Martha is more responsible than you," Hermes shot back. George couldn't argue with that. -- and slide up next to her. On the child's lower back, a spot not easily visible, Martha would give her small nip. Just long enough to make the child ill without arising concern of poison.
Hermes and George waited in silent anticipation, still perched on the roof of the house across. After what felt like an eternity, Martha slithered up onto the roof and retook her place wrapped around the cadeucus.
"Well?" Hermes asked.
It worked perfectly, Martha replied smugly. I bit the child, and sshe woke up ssshortly after with a fever. Nothing too sssseriouss, but enough that ssshe won't be traveling anytime sssoon. I heard the parentss make a phone call, to a sssibling, I think. He'ss going to come watch the child. The parentsss sstill have to go. Ssssomething about bussinesss.
"Well, that is unfortunate about the parents. But we've accomplished what we've come to do. Well done, Martha."
I provided moral sssupport, said George.
Several hours later, Hermes found himself back on Olympus, though not in the throne room. He and Zeus stood on its outskirts, overlooking New York City and all that lay beyond it.
"You're certain this is the right plane?" Zeus asked again.
"Yes, this is the plane she is scheduled to take." Hermes swallowed. "It isn't too late, you know. You can still change your mind."
"My mind is set."