Lumione 1

 Prologue

Hermione is recruited by the Unspeakables after graduation and is forced to go into the Undercover team which is a lifetime commitment. She has to say goodbye to her friends and family, relinquish her identity and basically cease to exist.

A mission goes wrong and in order to save her life, her magic has to be bound by a rune tattoo and her mind obliviated. Being Hermione Granger, she secures and maintains several specific images behind very strong occlumency shields.

Main story

Lucius Malfoy is release d from Azkaban (circa 2008) and is 6 months into his probation program which is being run by Harry Potter. This is the final test of the program: to book a family holiday (for himself, Draco, Draco's wife {whoever} and their 2/3 children), relinquish their wands prior to the flight and holiday as muggles for two weeks. 
N.B. Remove Narcissa from the equation in whichever way fits your story best.

Naturally, the Malfoy family are seated in first class which means the stewardess/air-hostess knows the passenger names. As the plane prepares for take-off, Lucius thinks he recognises the air-hostess but can't place her. He tries to ask Draco but his son is already dosing behind a sleep mask.

Once the plane levels off, the familiar air-hostess approaches Lucius with a drinks trolley.

"Good afternoon, Mr Malfoy. Would any of your part care for a beverage?"

"Miss Granger?" He asks, startled at the realisation that dawns on him.

"You're mistaken, I'm afraid, sir. My name is April Jones," the air hostess replied sincerely.

Lucius narrows his eyes but leaves it be for the moment, ordering a shot of whiskey.

He talks to Draco, later in the flight, and asks him if he recognises the air hostess, wondering if his own memory of Hermione Granger is flawed, although he doubts it. Draco confirms it's her.

They try to get her to admit who she is; Draco more than Lucius but she gets spooked by the things they're saying. Something along the lines of...

"You're a witch, Granger. We were at school together. You punched me in third year. You and your best friend saved the whole fucking world. How can you not remember?!"

It turns out they're staying in the same hotel, although Hermione/April only for two days. Over the course of the two days, they realise she really doesn't know who she is. Lucius and Draco follow her to the airport when she's departing and see her getting on the plane followed by another person they recognise who they thought was dead - Severus Snape. Lucius catches Severus's eye and sees a flicker of recognition before he boards the plane.

Unable to use magic, there's nothing Lucius or Draco can do until they return home. 

Back in England...

Severus reports to his superior that he was recognised by Lucius whilst on his temporary assignment for 'Operation April' - watching Granger. He's told to return and obliviate the Malfoys of their recognition of him and Granger.

Lucius is waiting for Snape, knowing what to expect if he's on some sort of mission. He confronts him and they talk. Lucius calls in an old life-debt to keep from being obliviated but can't stop Draco from losing memories of Granger. Severus doesn't explain everything... just that a mission went wrong and Granger had to have her magic bound and her mind erased of her magical life.

The Malfoy family return to England and Lucius can't stop thinking about Hermione. Knowing she has been obliviated again by Severus and won't remember their interaction on the plane, he starts to take an interest in her current life and realises that air-hostess'ing is just to make ends meet and she is actually a struggling artist  displaying her paintings in a gallery.

When he visits the gallery, her is shocked to see that her art work depicts scenes from her life in the Wizarding World. Hogwarts from various angles, Diagon Alley, Hogsmeade, the Hogwarts Express, portraits of Harry Potter, several Weasleys, Bellatrix, Dumbledore, McGonagall, Snape, even himself and Draco. There are realistic depictions of dragons, mermaids, unicorns... It gives Lucius hope that he can find the original Granger  still in her mind somewhere.

He buys her entire collection to make an impression on her and open a line of communication. Via his links to muggle publishing, he offers to get her interviews about her art to learn 'where she gets her inspiration'. Slowly they begin dating.

The night they make love for the first time, thanks to Lucius using sex magic, the power of the Malfoy family magic explodes through her with such force (given that he's fallen for her completely) that it latches onto the images in her mind and expands them into her entire history, breaking the obliviates that had been cast on her.

The reality of magic and her previous life burst free in Hermione's mind as she climaxes and as she looks down she is shocked and utterly dismayed to find herself riding Lucius Malfoy.