"Go away, Tuney," Severus Snape said as he moved to shut the door in Petunia Dursley's face as he regretted the fact that Lily had shown Petunia his house when they were children. Otherwise, his strong muggle repellent charms would have worked on her, because if Petunia was not a muggle, who was.
"You have to take him. Vernon is going to kill him," Petunia said, placing her foot in the door so that he wouldn't shut it.
Severus noticed the bedraggled very small child with messy hair and green eyes. It couldn't be, could it? That child of Potter's should be older by now, almost old enough to go to Hogwarts. This boy looked no older than six or seven.
"Who is this and why would I care?"
"I know you loved her, Severus. I have no love for her son, but I don't want him dead. You must take him for her sake."
Severus sighed and looked at the heap on his doorstep. If this was Lily's son, it was clear that he had been gravely mistreated. He knew he couldn't live with knowing he did nothing.
"Vernon knows where you live too. I would leave if I were you. Or use your magic to do something to protect him," Petunia sneered the word "Magic" in disgust.
"Leave him and get out of my sight. I don't want to ever see you again."
Petunia huffed, "Thank you, Severus," she said quietly and then quickly walked away without looking back.
That evening after Severus had healed Harry's many injuries, had the house elves buy him new clothes that actually fit, and gave him a (somewhat crooked) haircut, he observed the boy sleeping peacefully in his old childhood room. He had been seconds away from contacting Albus Dumbledore after Petunia left, but he didn't trust the old man. He hadn't saved Lily like he had promised him. He had clearly not left Harry in a safe and health household to be raised. The whole "Boy-Who-Lived" was bunk; he would not let his charge be pulled into such a circus based on a ridiculous prophesy, resulting in his becoming arrogant similar to his father.
His father, James Potter…Severus could not stand that the boy looked so much like his father; particularly with his eyes closed, there was nothing of Lily noticeable. How could he hide him but also make it bearable for Severus to look at him on a daily basis. He made up his mind and hurried to his potions lab.