Timeline:
Begins: After Deathly Hallows.
Epilogue: Not Canon Compliant.

Alterations to Canon:
Tonks survives the Battle of Hogwarts but remains in a comatose state.
Andromeda Tonks was killed by Death Eaters while on the run with Ted Tonks.

Pairings:
Beginning: Harry/Ginny and Hermione/Ron
Ending: Harry/Hermione and then Harry/Hermione/Tonks.

Story:
After the Battle of Hogwarts the survivors gather the injured and treat them, bury the dead and mourn for what was lost. Amongst the fallen is Remus Lupin but Nymphadora Tonks-Lupin is still alive - though catatonic and unresponsive. Eventually she is moved to St. Mungo's Long Term Spell Damage ward.

With no other relatives left to care for him Harry and Hermione, his godparents, are all that he has left and both of them are adamant that they'll stand by their promise. Hermione however has unfinished business with her parents and prepares to leave for Australia to find them, reconcile and bring them back - a decision made without consulting Ron who feels slighted and angers Hermione severely by suggesting that 'the muggles' could wait a while longer.

Harry refuses the Weasley's offer to move into the Burrow. Between the metaphorical ghost of Fred, a sober unfunny George, a still standoff-ish Percy's presence, Ginny's increasingly less subtle attempts to simultaneously resume and escalate their relationship as well as Molly's well-intentioned smothering and hovering are too much for him. He instead returns to Grimmauld Place.

It takes almost four months for Hermione to return with her parents, who had been angry, then reluctant and finally stressed by unravelling the lives and affairs of 'Wendel and Monica'. Ron never tried to reach her while she spoke almost every other day with Harry by phone. In fact she barely thought about Ron at all, let alone 'missing' him. A revelation that makes her uncomfortable.

Harry's determination to give Teddy what he never had - a good life raised by his godfather - remains unshaken but severely tested by his lack of knowledge and experience in caring for an toddler. Even with advice from several people he is stressed out and exhausted and after Teddy runs a fever and vomits he takes him to St. Mungos. They visit Tonks' room and Harry is surprised when Teddy instantly stops fussing and wailing and falls asleep on the bed next to his mother in short order. After that he and Teddy are visiting her for several hours at a time at least three times a week. Harry reads to Tonks and plays games and sings songs with Teddy.

Things don't get any better on the relationship front for either Harry or Hermione regarding their respective Weasleys once Hermione returns to Britain and moves in with Harry and Teddy. Two stilted dates on each couples part and the third dates called off when Hermione lands a job - as Hogwarts' new assistant librarian - and Harry has to change his schedule to look after Teddy. Ron more than Ginny, but both nonetheless, are becoming increasingly uncomfortable about Harry and Hermione sharing a home and raising a family.

Arguments, broken plans, uncomfortable dates and escalating jealousy on the part of the Weasleys rapidly sour both relationships. Worst of all both Harry and Hermione feel guilty because the Weasleys' jealousy isn't entire unjustified, both of them having experienced profound emotional moments witnessing each other bonding, raising and loving Teddy.

Ginny approaches Hermione almost accusing her of monopolising Harry's time and attention, that she is Harry's girlfriend, so why does Hermione always factor into Harry's life before she does? Defending that it's all about Teddy provokes Ginny into blurting out that they should put him up for adoption. The idea of Harry losing Teddy and the joy that having Teddy brings him incenses Hermione like nothing else. She also realises that the only future she imagines features the situation she's in now, sharing a home with Harry and Teddy, they ARE her home.

Not long after that Harry dumps Ginny, refusing to go away with her to a Quidditch training camp in Ireland for a month. This only serves to make Ron more insecure who sees it as one less obstacle to Harry taking Hermione away and he straight up accuses Hermione of 'playing house' and Hermione's initial silence and lack of immediate denial as she questions if Ron is right only seem to confirm it for Ron. Ron snaps and tells her it's over and after a good cry Hermione finds she doesn't feel very bad about the relationship ending.

(Out and out bashing of Ginny and Ron would undermine a lot of the plot-useful uncertainty, hesitation and necessary build up of Harry and Hermione's eventual relationship)

Days pass, Ron and Ginny both make attempts to fix things up, but neither Harry nor Hermione accept. Hermione is constantly plagued with doubts. She wants to talk to Harry about her feelings and thoughts but is equally fearful that his break up with Ginny wasn't like hers with Ron and doesn't feel the temptation or want the same thing she has begun wanting. Distracting herself with work and taking Teddy to visits with Tonks, she begins to put a little distance between herself and Harry.

Things change dramatically thought when one day at Hogwarts while visiting Neville, the new assistant Herbology Professor, she meets an awake and aware Alice Longbottom. After almost 17 years trapped in a coma and then a dissociative state after limited success by Healers at St. Mungos she suddenly just 'came good' the day after Bellatrix Lestrange met her end at the Weasley Matriach's hands. Neville laments that his dad didn't awaken and he suspects that Rastaban Lestrange, who escaped from Hogwarts (and the UK) after the Dark Lord fell, might have been the one to cast the same curse on his father.

Hermione knows that Rastaban was the one last seen fighting Tonks.

When she shares her insight with Harry (standing in Tonks' room at St. Mungos) sees their first real fight since they took the job of raising Teddy. Harry wants to go off and kill Rastaban but Hermione, terrified of losing him, instead accuses him of abandoning Teddy. Harry says he's doing it for Teddy, so he can have his mother back. That if it were the case that Tonks was being held captive by some Death Eaters she'd never question his plan - and in fact that's exactly the case. Hermione retorts angrily that she's as good a mother to Teddy as any real mother. Harry angrily disputes that as an orphan he has an entirely different view of how replaceable parents are. That just because she sent hers away...

He stops himself the moment he sees the pain on Hermione's face and apologises with Hermione following suit a moment later, glomping Harry in a hug and blurting that she's afraid to lose him, to lose their family. Harry kisses her and they confess their feeling to each other while Hermione slowly comes around to accepting that Harry owes this to Teddy and Tonks.

Harry recruits some allies: Neville (dead-set on the slightest chance to restore his father), Susan Bones (who wants Rastaban dead for murdering her friend and fellow 'Puff, Megan Jones) and surprisingly Daphne Greengrass (whose parents were killed by the Lestranges after they were caught sheltering half-blood and muggleborn friends who were fleeing the Ministry's purges) who has become a Hit Wizard specialising in bounties on Death Eaters and Snatchers wanted for war crimes.

A month later and Rastaban, or what's left of him, receives a fond farewell in the form of a premature cremation, courtesy of Daphne. The next day Tonks wakes up to Harry lying in the next hospital bed, with his own wounds from his adventure. Teddy greets her with a babbled 'mum', bringing her to tears.

Like Alice and Frank (who has also awoken now) she was partially aware of what went on around her while she was catatonic and so knows a lot of what has gone on before and while she was out. She remembers (as though a dream) the presence of all three of them in her life over the last year or so and most importantly knows of Harry and Hermione's loving care for Teddy and what they gave and risked to bring her back. Her emotions are a rollercoaster for the next two weeks while she undergoes rehabilitation and returns the favour of reading to Harry while he's recuperating. On some level she's known of Remus' death since it happened but now those delayed and muddled emotions are bursting to the surface.

She most definitely has no intention however of parting Teddy from Harry or Hermione and with her apartment long since packed up and its lease elapsed she moves into Grimmauld Place too.

Tying One On:
Tonks' innuendo and lewd encouragement hastens Harry and Hermione's procrastination about starting a physical relationship with Tonks and Teddy present - especially her threat to morph into one of them and crawl into bed with the other if they don't release some tension soon. Later she revels in plumbing Hermione for details as she lives vicariously off their relationship. Tonks' ""helpful suggestions"" and ""detailed instruction"" to an inexperienced and naive Hermione about how to drive Harry wild in bed provokes confused and aroused feelings in the younger witch whose vivid imagination can't help but picture Tonks in such explicit scenarios and roles as she describes them.

Likewise Harry finds himself ashamed of his eyes occasionally straying to Tonks whose ever-flirtacious nature, coupled with watching her mothering Teddy as well as her habit (guileless though it mostly is) of under-dressing while at home gives him plenty to look at.

Some time later a holiday that was originally intended to be for Harry and Hermione to get away eventually ends up becoming a holiday for all four of them and during their trip circumstances conspire to open Harry and Hermione's minds to the idea of including Tonks in their relationship and before they've returned to England the couple have become a thruple.

Epilogue:
Harry, Hermione and Tonks with Teddy and his two siblings, Harry and Tonks' daughter and Harry and Hermione's son.