It’s strange how easy it is to take future knowledge for granted when re-reading a book you’ve read again and again. Take, for example, the first chapter of Goblet of Fire. A first-time reader will have never met the other Tom Riddle yet. While the name should of course be familiar, and a reader with a good memory might recall that Voldemort was named for his father, there’s no assumption yet that he murdered his muggle father and grandparents, or that it’s in their abandoned house that he’s lurking for the moment, scheming to return.
The mystery of the Riddles’ death is sort of a foregone conclusion, if you’ve already finished both Goblet of Fire (for the Unforgivable Curses) and Half-Blood Prince (for the Tom Riddle backstory). But while the first-time reader might guess it’s unlikely they were killed by a muggle gardener, and even pick up on the clues that it was Voldemort, they wouldn’t have the certainty of how and why he murdered them. The medical report – “none of the Riddles had been poisoned, stabbed, shot, strangled, suffocated, or (as far as they could tell tell) harmed at all. In fact (the report continued, in a tone of unmistakable bewilderment), the Riddles all appeared to be in perfect health – apart from the fact that they were all dead” – is a perfect description of Avada Kedavra, but since that won’t be explained until later in the book, here it’s just a hint that they were killed by magical rather than muggle means.
The “teenage boy, a stranger, dark-haired and pale” who the Riddles’ gardener describes to the police is undoubtedly the younger Tom Riddle. That much is evident from the start. I’ve written before about young Voldemort’s tendency to frame others for his crimes, and here, not one but two innocent people take the blame. The muggles accuse Frank, the gardener, while the wizards believe Tom’s uncle, Morfin Gaunt , to be guilty. But that won’t be revealed until Half-Blood Prince. For now, the only thing linking these murders to the magical world are the strange circumstances and the links with the boy who grows up to be Voldemort.
On the other hand, the things that confuse Frank as he listens in on Voldemort and Wormtail’s conversation make perfect sense to anyone who’s read the three books before. We know who these two men are, and we instantly recognize Harry Potter’s name. “Quidditch” and “muggles” are not nonsense words for us. We may not recognize Bertha Jorkins’ name, but we have no reason to believe – as Frank does – that the two men are speaking in some kind of code. Listening in on their conversation gives us important clues as to what is coming, most importantly that Voldemort is after Harry again and that he has a plan to get him away from the protection of Hogwarts.