When Tiffany woke up the next morning, the solution to her predicament was quite clear. Eskarina Smith would definitely know quite a lot about alternate dimensions, and could probably tell Tiffany something about the one that Harry came from.
After posting the letter, Tiffany was a bit uncertain about how to go about her daily rounds of the Chalk with a baby. Eventually, she managed to rig up something like a booster seat to her broomstick and simply towed Harry along on it.
The days passed quickly, with Tiffany being very busy with her usual witch business as well as taking care of a small child. After about two weeks, though, Eskarina's reply to the letter arrived in the mail. She apparently had visited that particular dimension before, and was more than willing to impart her information on the matter.
The basic gist of it was that there was a very bad man there that wanted Harry dead, and Harry was some kind of Chosen One. Eskarina also said that although the wizards there were very good at magic, they weren't the sort of people that should be trusted to raise children. The letter also went on for a while about various theories about dimensions, and Eskarina's latest research, but Tiffany mainly ignored all of that because that was what most of her letters looked like.
XxX
Soon, life began to take on a routine. Harry followed around Tiffany on her broomstick, and played with the Nac Mac Feegles when he got the chance. Whenever Tiffany went to visit Preston in Ankh Morpork, Harry would be taken to Unseen University to learn how to use his magic.
About nine years passed in this manner, with no horrible monsters to interrupt it. Tiffany and Eskarina still wrote to each other, and much information was exchanged about the dimension that was soon found out to be Roundworld. It was not quite as magic-less as Ponder had originally thought it to be.
After several incidents at the University, the wizards there soon determined that Harry was really, really bad at magic. Horrible, even. Harry still went to the University anyways, because he liked it there, and Mr. Stibbons let him play games on Hex, and mostly because no little boy wants to see their Mum getting romantic with anyone, even a very smart doctor-in-training like Preston.
This routine continued until Harry was about eleven years old. Just after the day when Tiffany had guessed when Harry's birthday was, a very strange letter was delivered to them...
Author's Note: So sorry to leave this for so long! I meant to write some more on vacation, but was distracted by the sheer awesomeness of Disneyworld. I'll try harder to get more updates sooner, but I can't guarantee it, mainly because I'm just making up the plot as I go along.