7th year, canon through OotP, and then it cherry picks, because why the hell not?
Dumbledore is still alive and, after Hermione is attacked in the halls of the school, he comes up with a plan he is ever so sure will keep her safe... amongst other things. His Potions Master must be bonded to her. Of course. It's the only thing for it. It's not like Albus has ever been wrong before.
Severus is understandably chuffed.
But maybe it won't be as bad as he thinks. Sure, because he's typically lucky.
Let's do this the shorter, if expositiony, way so we're all starting on the same page, so to speak (non-canon elements are in bold). Picture, if you will: It's seventh year now. HBP didn't quite happen that way, many of its events are being spread over 6th and 7th years, and we're ignoring large parts of DH except for the background information and insights it provides on the characters, because frankly the book made me a little miserable, and life's too short. (Try to love me anyway, ta. I'm mostly lovely... Yes, even if I do say so myself.)
Back in sixth year, Harry snagged the Half-Blood Prince's textbook, made enthusiastic use of it to ingratiate himself to Sluggy, the bastard (ten points to Gryffindor for being enterprising, cheers!), and Sectumsempraed Draco from stem to stern. True to form, Dumbledore took an Oath from Draco and bound him to silence and both he and Severus are more enamored of dear Harrykins than ever. This seriously pushes a number of Severus' buttons (we all know how many of those he has), and he's feeling frightfully stabby.
Harry's use of the Felix Felicis Potion to pick Sluggy's brain revealed two crucial things, the first, that Slughorn did in fact talk to Tom Riddle about Horcruxes while he was a student, and the second, that Sluggy immediately high-handedly criticised Horcruxes as a solution if only one could brew Salazar's adaptation of Merlin's Invincibility Potion instead. Whatever that is. Hmm... Dumbledore sets Harry on the first problem and Severus on the latter, keeping both in the dark about the other's mission. Because that's how he rolls. Nit.
After much searching, the recipe for the potion is found. If only that were the end of it...
Severus' first problem is to figure out what they need to brew the potion. It's not like the recipe is in plain text; that's for losers. Or Muggles. (Although the Ministry now admits: they are not as stupid as initially thought...) Some ingredients are commonplace, most are hard to come by, and a small handful he just can't seem to figure out. How promising. Additionally Albus is now certain that they'll need several magical artefacts for the brewing, too, not that he knows what they are. The memories he collected and shared with Harry sixth year do double duty, to find the Horcruxes and help solve the brewing problem.
One such memory was of the very rich Hepzibah Smith, an avid collector of magical antiquities. The memory revealed her showing Riddle her two most prized possessions, Salazar Slytherin's locket and Merlin's silver stirring rod. While that's no proof, Dumbledore strongly suspects Tom stole them and used both in recreating the Invincibility Potion, as the artefacts were never recovered on her death.
Albus has already found the ring that Tom stole from his uncle where it was hidden in Gaunt the cottage. He's lifted the curse, so that Severus can safely use it to brew, but sadly only after he himself was fatally cursed. His arm continues to wither, and he thinks he hasn't much longer now. Unfortunately, there's still so much he needs to figure out.
Almost equally traumatically, WonWon spent a large chunk of last year snogging LavLav, but eventually crumbled under the weight of that and sought canonical refuge, well, not quite in Hermione's arms, but, y'know. Sadly, he's still not man enough for her, that was going nowhere fast, and when Hermione wanted to turn in Harry's Potions text after he attacked Draco, Ron again accused her of betrayal ('Firebolt' anyone?) and ghosted her the rest of the year and most of the summer. Tosser. She may be used to it, but it's getting old fast.
Early in June, suitably recovered from Harry's attack, Draco went back to scheming. It was only a question of time. He attempted yet another convoluted plot to smuggle yet another dark McGuffin onto school grounds, a diabolical draught procured courtesy of Dogweed and Deathcap, Hogsmeade. In a flash of inspiration, the Imperiused courier he selected this time was none other than his cousin Nymphadora Tonks, stationed in town. One would think misusing an Auror in this fashion would lead to better results than a barmaid or fellow student, but then one would also need to be unfamiliar with the targeted good lady's ungainliness. Alas, Draco doesn't know his cousin very well.
It went as it had to.
With the mysterious substance stowed theoretically safely in her pocket, Tonks and Kingsley were drawn into a skirmish with Death Eaters while on patrol in which she suffered a minor injury. Unfortunately, as she was hexed she stumbled, fantastically, the phial broke, the gelatinous gloop splashed onto her skin, and she collapsed in a writhing, shrieking heap on the ground. Heeding the call of Kingsley's Patronus, Remus and other Order members quickly arrived to help, and the attackers were soon dispatched. Sadly, her friends were at a complete loss what to do for the young witch.
In short order, she was brought to the school's Infirmary. Severus was out gathering ingredients for his... secret project, and Poppy proved as unable to help as the others faced with this strange, unknown substance, and briefly all feared the worst. Tonks, however, is naturally blessed with a great deal of luck, both good and bad, and the properties of her malleable skin served to enable her to ultimately shake off a dose that would almost definitely have killed almost any other witch or wizard without her gifts. It was a close-run thing, but soon she was up and about again, with a ready 'Wotcher' on her lips.
Not long thereafter, that wasn't the only thing on her lips.
Once the dust settled, realising life's too short, she told Remus she loves him and to stop being so thick. The scare of almost losing her seems to have finally brought the werewolf to his senses, and he swept the young Metamorphmagus into his arms for a good snog. They were married in a small ceremony in July.
As no one was seriously injured, Albus again turned a blind eye to Draco's machinations.
Severus schooled the boy to sell Tonks' injuries as a deliberate and very serious attempt on her life for her disloyalty to the Dark Lord and the pure-blood cause. Draco wouldn't dream of accepting such a thing from a family member... This won him a reprieve for his numerous failures on the Headmaster's execution front, and Voldemort found himself ostensibly sufficiently impressed by his actions that he finally deigned to free Lucius and his fellow inmates from Azkaban as a reward. How lovely. Severus half suspects this was meant as a punishment... Lucius and Draco probably feel much the same about it themselves. The feeling is only reinforced when You-Know-Who avails himself of Lucius' wand in addition to his home.
As the lot of the freed Death Eaters now find themselves hiding out under a veil of very black cloaking magic at Malfoy Manor, there is indeed good cause to believe this is by no means a reward. Only when they gain control of the Ministry will they truly be free. It can't happen soon enough. But in the meantime, as long as the Prophet's on their side... And officially, of course, there hasn't been an escape. Again.
The Battle of the Seven Potters took place pretty much as we know it, except the suggestion came to the Order members directly from Albus. Harry distributed what was left of his Liquid Luck to his friends who played the other 'Harry's, and they arrived safely (except for Mundungus who bunked off). Sadly, Hedwig and Moody did not. Harry blames himself, as he does. Severus had to maintain his cover and flew masked. He did not inadvertently slice off George's ear, possibly because of the Felix Felicis Potion, but there may have been other casualties.
Just the day before his wedding, on Harry's birthday as it happens, while on a break for lunch, Bill encountered a small handful of You-Know-Who's men snatching Garrick Ollivander from Diagon Alley. Curious about the destruction of Lucius' wand in the Battle Over Little Whinging, ol' Tom had some questions for him... Bill intervened, and was injured by Greyback before his Patronus could summon the twins to his aid. Tonks was patrolling nearby, on a new assignment given the school hols, and was able to hold the attackers at bay until Fred and George answered her call and arrived to help. There were no further injuries, however they were unable to prevent Ollivander from being taken. Remus threw a wobbly when he found out Tonks was in another battle, poor chap.
Bill and Fleur's wedding was put off for a couple of weeks until he was recovered. Certain family members were much impressed when Bill's scars failed to frighten off Phlegm, erm, Fleur. They married shortly before school resumed in a beautiful and largely uneventful ceremony.
WE NEED BETRAYAL HERE... (This and the ghosting would be the placeholder equivalents of Ron's walkout while on the camping-trip-that-would-not-end-and-made-me-sad.)
At the beginning of term, it was announced that the Muggle-raised and Muggle-born students will be required to wear badges marking them as such, and have to register their wands, regardless of age. Umbridge was most keen to see to that. The spells put on their wands have suspicious echoes of limiters and traces, and Hermione was not best pleased. She kicked up a massive fuss, which (typically) accomplished bugger all. Nevertheless, Harry politely joined in. He can be good that way.
Harry, in fact, championed her cause so enthusiastically, that he went to Luna's father and gave the Quibbler an exclusive interview, in which he spilt all (he secretly prefers the colour green to red), trash talked Dolores and swooned rather childishly over his favourite Quidditch Players. Interviewer bias may have played a role in some or all of that, but certainly in the rhapsodising about Gwenog Jones. (While Ginny agreed with the statements in principle, she was a mite put out by the specifics.) Somewhere in there he probably decried the Ministry's methods for targeting the Muggle-born and -raised. Not that many noticed.
Naturally it didn't help, but it ruffled a few feathers. Particularly the colour thing...
Ron, not entirely unreasonably, adamantly refused to support Hermione's campaign. He pointed out he has his family to worry about, and can't afford to endanger them by unnecessarily being seen to be a trouble maker, especially as what the Ministry was asking of her wasn't so bad and, face it, she wasn't being particularly successful anyway. To this day she continues to blame lack of support primarily for that last, so while she could (sort of) understand his position, she couldn't forgive his lack of... well, support. They (frequently) manage to keep their interactions reasonably polite, but the cracks in their foundation are irreparable and will only get worse over time.
Severus completed their sixth year as the DADA instructor, but as the position is still cursed, he couldn't remain. Simples. Sluggy's lax attitude towards discipline in his Potions classroom meant a major accident in the Ravenclaw / Hufflepuff O.W.L. class seriously injured a number of students and permanently depilated Horace's own eyebrows. Far too proud to be seen in public like that, Merlin forfend, and given the increase in parental complaints, not to mention the worst Potions O.W.L.s and N.E.W.T.s average scores in over fifteen years (but probably mostly due to that first bit, really, priorities being as they are), Slughorn did not return for Hermione's, Ron's and Harry's seventh year, and poor Severus finds himself back in that thrice damned Potions classroom. Once again, he's massively chuffed. His joy knows no bounds.
The seventh year began with the Malfoy family in even more desperate straits than when we saw them in the canonical HBP 6th year. Draco has been given the stepped up 'kill Dumbles' suicide chore this year. He's done faffing about with cursed trinkets and poisoned oak-matured mead like last year. Severus has sworn the Unbreakable Vow to aid and abet or die. It's of little consequence really, as Albus had already conscripted him to similar service. Life is a bed of Fanged Geraniums. Particularly toothy ones. Nothing gummy here but those damn trunks of Draco's, which are proving as frustrating to him in this story as they were in HBP. And again Draco is inexplicably happy to be as slow to repair it as he was in canon. (What? It worked for JKR...)
Harry's paranoia is ramping up. He may be right, Malfoy may in fact be a suspicious wanker (No, really, he actually is, but he's having a really shite life, what with the permanent Houseguests of Evil and all, and he's just all around falling apart at the seams. Positively frayed...), but goodness is Harry ever driving everyone bonkers with it. Dealing with the restrictions and probable traces placed on Muggle-borns (like Hermione) and Muggle wards (such as Harry) means his snooping about is somewhat limited, but fortunately the Invisibility Cloak balances out some of that.
The Ministry is pretty much laced with Voldemort's supporters. There are thankfully no camps for the Muggle-born, yet, and they are not barred from attending school. The Death Eater attacks aren't as violent or as widespread as they were in HPB, but they are steadily increasing in magnitude, and the writing's on the wall for the literate. Sadly those seem few and far between in the wizarding world. (Personally, I always thought people were less likely to balk if the process had been a slower one, so here it is.)
J.K. Rowling owns whatever you recognise. I may not be happy with some of canon, but damn if I don't sincerely think she's brilliant. I wouldn't care as much if she hadn't made some truly engaging characters. So all the props and then some to her, and a heartfelt thanks for letting me play with her world.
Well. This isn't particularly fluffy or light. Sorry. But it's also not especially dark. Read, don't read - whichever, but please don't flame. Tags are used for a reason. Do us both the kindness of taking them seriously.