Vernon Dursley gets a letter from Hogwarts. Story starts two days after the end of "Return to Privet Drive." Part 3, Kings Cross and the Hogwarts Express.
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September 2028. Harry accompanied the Dursleys to see off Vernon on his journey to Hogwarts. Vernon had a trolley laden down with all his Hogwarts things, Harry the cat was still perched on Vernon's shoulder.
Dudley was still very doubtful about Platform 9 3/4. "Look Harry, there is 9 and 10 but no 9 3/4."
Harry whispered in Vernon's ear and he ran pushing his trolley towards the wall and disappeared!
"Where did he go, what have done with my son?"
"Don't panic Dudley and Patricia. Both of you take hold of my hands." Harry walked them onto Platform 9 3/4, there they could see the gleaming steam train, the "Hogwarts Express". Vernon said "Mum and Dad, isn't it fantastic."
Harry "OK, the train is leaving in five minutes, time to say goodbye." Vernon hugged his parents and then Harry whispered in his ear "Have fun at Hogwarts, say hello to Hagrid for me and get him to tell you what he did to your father the day I first met Hagrid..."