This was about the point that I knew I was going to like your Petunia...
Mister Dumbledore,
You will make arrangements for me to attend my sister’s funeral or I shall leave the child on the steps of a police station. You took her from me in life, you will not deny me my chance to say farewell.
Mrs. Petunia Dursley
...and could already foresee how she and Snape would get along. That "Mister" - just perfect.
I love stories that take canon and flip the perspective entirely. Here, Snape and Petunia's feelings about Harry move entirely out of the realm of cartoon and into something sadly believable. I really enjoyed how their relationship grew visit by visit, summed up so aptly by this:
"Why are we here?" she asked.
"Because we can't let her go," he answered, and he handed her a handkerchief.
Poignant, understated, and beautifully characterized. Well done, Mystery Author.