Disclaimer: HP not mine, only the plot and new characters are. Will be as DH-compliant as I am interested in.
His Mistake
Prologue
... The last trace of steam evaporated in the autumn air. The train rounded a corner. Harry's hand was still raised in farewell.
"He'll be all right," murmured Ginny.
As Harry looked at her, he lower his hand absentmindedly and touched the lightening scar on his forehead.
"I know he will."
The scar had not pained Harry for nineteen years. All was well.
Or so he thought.
Harry James Potter glanced at his pretty wife, Ginerva Molly Weasley Potter, her hand holding onto their youngest and only daughter's hand, who was waving frantically at the Hogwarts Express that was carrying her cousins and brothers towards the school of magic. Remaining on the platform were his best friends; Ronald and Hermione Weasley, their young son Hugo, the Malfoys and his godson Teddy Lupin when popping sounds surrounded them as Auror robed officials moved forward to grasp the brunette in the group roughly.
"Bugger off!" Ronald Weasley cried out as his wife's arm was jerked out of his loving grip as two special-unit Aurors, held onto his wife's arms with firm determination. His ten-year-old son yelled as his mother was quickly spellbound and held in place by one Auror while the other cast the spell and glanced over the others. The Auror's eyes seemed to be trained on something from behind Harry, who quickly turned, wand out to see two black robed figures come from behind a pillar, features hidden beneath the hoods.
"What is the meaning of this?" Harry demanded, pushing his wife and daughter behind him, just in case. Draco Malfoy and wife stared at the Aurors audacity to do this in such a public place, as lingering parents of students that were leaving seemed to pause to stare at this development. Teddy Lupin gapped at the Aurors as if they had gone mad to be seemingly arresting his adopted 'Aunt' Hermione.
Ignoring the Hero of the Wizarding World, the second Auror addressed only the curly-haired brunette, "You are under arrest for attempted murder, false impersonation and using the Dark Arts."
Ginny gasped from behind Harry, while Ron was seeing red as well as having his face resembling a tomato as the accusations were announced. Lily began to cry and Hugo whimpered as he held onto his father's right arm, which was clenching his wand.
"On whose authority are you arresting Hermione? I know some very important people..." Harry began, his wand hand tightening.
"We know who you are, Mr. Potter and do not think this matter concerns you," the second Auror, a young curly dark haired fellow informed, "as Hermione," the name was spat as if disgusting, "has a date with our interrogator."
The frozen in place the Hermione in question seemed to take on a look of horror at their words. Without another word, the two Aurors apparated with Hermione out of Platform 9 3/4 to the Ministry. The two figures that had yet to be made known to them stepped forward.
"I am not the least bit sorry to say that she will get what's coming to her," a young female voice came from beneath one of the cloaks.
"Identify yourself! Making false accusations is a six month sentence in Azkaban." Harry told the two.
"Please," the lightly accented American tone came again, as the hood to the cloak was lowered to show a very pretty young girl of eighteen with Gypsy black curls and amber eyes flashing, smirking smugly at Harry with such enjoyment that Harry was momentarily taken back, "go ahead and try, Mr. Potter. I am sure the real Hermione Granger would love to see her daughter in Azkaban."
"What?!" Ronald and Ginny shouted.
"Oh," the girl looked irritatingly innocent, "did I not have that mention in the charges? Your wife, Mr. Weasley," the girl's distaste for the Weasley name was evident in her tone, "has been falsely impersonating Hermione Granger for the last eighteen and a half years. A crime punishable by no less than a lifetime sentence in Azkaban according to British Wizarding Law. On top of the other charges..."
"Listen here, you smug little..."
Ronald moved to cast a spell with his wand, when the other cloaked figure pulled out a wand and simultaneously disarmed him.
"Expelliarmus!" The words so forceful that Ron flew back, nearly landing on the railroad tracks, his body causing a horrible crushing sound as bones broke. Hugo screamed.
An enraged figure moved forward, an feminine hand cast out to move the masses to the side as the unidentified assailant stalked up to her victim, even as Harry was ushering Ginny to take the children home and running towards the fallen Ron. He was unfortunately unable as he was instantly petrified and fell like a stone as the young girl cast her own spell.
"Stupid, complacent Gryffindors," the girl muttered, as Harry landed on his face, his wife and the children had already popped out of sight, while Draco had sent his wife homeward while his cousin remained with him trying to figure out what was going on. Others on the Platform fled.
Pulling back her hood as she approached the injured Ronald Weasley, the matured features of Hermione Jean Granger appeared to the man she was supposedly married to, who stared at her with blue eyes filled with confusion. Her rage was clear on her face as she trained her wand on his body.
"Try and curse," she started, "my daughter again and I will send you to St. Mungo's in a matchbox, Ronald Bilius Weasley."
"Hermione?" Ron questioned, coughing loudly as he couldn't seem to catch a breathe.
"Recognize me, do you? You should since your 'wife'," Hermione shook her head in anger, "has been trying to be me for years. Using my body as she goes about her daily business. Ruining my life and reputation and not a single one of you knew the difference. You disgust me."
Turning on her heel, she moved away from him, staring down at Harry.
"Some hero you are, Harry," she said, before rejoining her daughter. Passing by Draco Malfoy and Teddy Lupin without a glance.
The girl blew a kiss to them.
"Be seeing ya."
As the two apparated, Teddy gave the countercurse to Harry, helping his godfather to his feet while Draco whistled low.
"And I thought Granger had lowered herself to marry a Weasley," Draco commented as Harry and Teddy helped Ron sit up, blood being coughed up and soaking his shirt, all three staring at him, "but now I guess she had the good taste to not marry you, Weasel. Good for her."
With that Draco returned to his own home, amused in a way he hadn't been for years. Seemed the 'Golden Trio' was going to get the karma they so richly deserved.
Inside a holding cell in the Auror division of the Ministry of Magic, the person wearing Hermione Granger's features buried her head in her hands, sobbing as she knew the world she had so carefully constructed was about to come falling down around her ears.