Time Turners: The Biggest Plot Hole in the Series?
The complaint
The Time Turner is introduced in The Prisoner of Azkaban so Hermione can attend extra classes. It becomes a plot device when she and Harry use it to save Sirius and Buckbeak. And then it raises a question the story never fully answers: if time travel exists, why doesn't anyone use it to prevent Voldemort's rise, save the Potters, or undo any of the tragedies that follow?
The films make this worse by showing the Time Turner as a simple, widely available device. The books are more careful, establishing that the Ministry controls them tightly and that they're dangerous, but the question lingers.
The answer the books give
The time travel in Prisoner of Azkaban follows a closed-loop model: Harry and Hermione don't change the past; they fulfil it. Everything they do in the time-travel sequence already happened the first time through. Harry was saved by a Patronus the first time because his future self cast it. Buckbeak was never actually executed; the executioner's axe hit the fence.
This means you can't use a Time Turner to change history, because anything you do has already been done. The past is fixed. You just might not have seen all of it the first time.
The fifth book adds a further safeguard: the entire stock of Time Turners is destroyed during the battle at the Department of Mysteries. This is widely read as the author closing the door on a device that threatened to undermine every future conflict.
Why it still matters
The Time Turner debate is really a debate about what kind of story Harry Potter is. If it's a puzzle story, where every tool should be used to its full logical potential, then the Time Turner is a problem. If it's a moral story, where the point is not to avoid suffering but to face it with courage, then the Time Turner is a thematic statement.
The message is that you can't fix everything by going back. You have to live forward, with the choices you've made and the losses you've suffered. That's what Harry learns across seven books, and it's what the Time Turner, by being limited and then destroyed, reinforces.