Every hundred years, it is mandatory for a witch, warlock or wizard to visit the mortal plane and perform one good deed, summoned by a human wish chosen at random. None of them like having to do it....visiting Earth feels like being sent to prison for a day. They don't care much for mortals, or think much about them, because the way they see it they're doomed anyway -- but out of obligation, or to make themselves look good, or to throw humanity a bone in the same manner the homeless are given a Thanksgiving dinner -- they visit Earth and "help" someone. Then they leave for home and their role is forgotten.

Ordinarily, this would have been the routine case for Winnie Goodwin, whose number came up when a member of the Harper Family in Connecticut wished for help. She was discovered by the family patriarch five minutes into her assignment, but fortunately, quickly came up with the cover of the Harpers' new housekeeper.

To the Harper kids, Winnie was amazing, but where she comes from she is merely average and run-of-the-mill (though she has a very strong spark, which is a witches' term for innate magical power). Winnie feels neglected and unappreciated in her homeworld, and was taken aback when the Harpers expressed such an interest in her existence. Not only that, but the more embarrassing calamities she caused, the more they loved her! At the end of the day, Winnie found she couldn't leave her new assignments -- who were now her new friends.

The children's father, Thomas Harper, entrusts Winnie with care of his house and protection of his children -- if only he knew the truth. Though she may be a young adult (just 349), personality-wise Winnie is just another one of the kids. She takes their side in family arguments, and she has the same wants and desires they do. And she doesn't hesitate to use her magic to make them happen! With Winnie now as a member, the Harper family (minus Thomas) lives an amazing life of adventure, action and peril, topped with ridiculous levels of wish-fulfillment.

One isn't sure what you would call a witch-adolescent relationship -- it defies categorization, but whatever it is, it's strong. Winnie turned out to be a missing piece in their lives that is now irreplaceable. The Harper family was rather dysfunctional before Winnie joined them. After she arrived, the children became highly functional and started caring not only for Winnie, but for each other.
Gene is, in many ways, a Mini-Winnie -- her sidekick, her partner in crime, as well as a bad influence on her. Who better than an imaginative child to test the warped limits of magic?

Quite often the path out of a sticky situation involves doing something the other Harpers would find awkward or embarrassing. Gene doesn't even question it. With his young, scatterbrained mind, he never finds anything Winnie does unusual, and in fact keeps feeding her ideas better than what she could think up. Gene is Cowboy Bebop's Radical Edward mixed with the resourcefulness and determination of Game of Thrones' Arya. He may seem goofy and innocent, but few kids his age really are.
Jessie may be the closest thing to a grown-up the Harper family has. Though just 14, she is highly intelligent and book smart, and takes leadership roles in the Harpers' adventures. She and Winnie are deeply interested in the knowledge the other possesses -- Jessie's of the earthly world and Winnie's of the ethereal and magical. They make a good team in perilous situations, and they have become true best friends.
Imagine if Han Solo had no marksmanship, laughable piloting skills, and Greedo shot well before he did yet he tells a different story. That's Robb Harper, the eldest and most deluded of the gang. Despite the humiliations, defeats and cheek-slapping rejections he constantly suffers, nothing ever seems to rattle his ego or shake his rock-solid belief in his perceived status as a macho, super-suave lady killer. The other members of the family just roll their eyes and put up with him.
With the absence of the Harpers' mother, it's solely up to their father Thomas to be the breadwinner in this family -- and he wins a ton of bread! The Harper family isn't exactly mansion-dwelling, 1% rich, but they live comfortably enough thanks to Thomas's high executive position. (They're well-off enough to afford a housekeeper, anyway.)

Thomas is unaware Winnie is a witch, and can never find out. For one thing, he was never authorized to know, and two, Thomas finding out about Winnie's powers could put a permanent end to the Harpers' adventures. He definitely wouldn't approve of the shenanigans they get into on a daily basis. Winnie might even be fired, and then they'd never see her again!

Fortunately, Thomas is so absorbed in his work that he is always at the office, and absent from the house constantly. This may be why Thomas's wife left him -- but we're speculating. You aren't going to get any answers out of the kids; they get awkwardly quiet about this subject.
To protect her own identity and those of her friends, Winnie will sometimes take on the guise of a completely different person. These people have built their own separate lives and backstories, and reputations -- except for the Harpers, no one knows they're all Winnie. Typically, these alter-egos come with ridiculous, obviously phony names that no one ever questions.
Fraulein Frankfurtress, revolutionary and freedom fighter
Anne Chovy, globetrotting heiress archaeologist
Liz Lolly, high school cheerleader
The most demented and unhinged of Winnie's aliases. When she breaks out Liz, you know you're in for it!

Winnie's magic broom is always with her and can be brought out at any time with a twirling wrist motion. It extends in length depending on how many passengers are riding, and can take them anywhere in the world in a relatively short period of time. While riding the broom, Winnie and the Harpers are invisible.
Winnie gets a bit nervous around mirrors, and for good reason....mirrors are a major weakness for any magical creature. Mirrors and magic are like oil and water; they repel each other and can't mix. If Winnie isn't careful, a spell could ricochet off a mirror and land where it wasn't supposed to.

In addition, if a witch is imprisoned within a mirror, it's impossible for her to escape unless someone or something lets her out. Then if the mirror is smashed, the witch ceases to exist. This fate is Winnie's greatest fear.
Because dogs didn't like her first! They go crazy whenever she approaches them! They must sense something eerie they don't like, because they bark like mad and struggle against whatever leash or fence is holding them back. Sometimes there's neither, and Winnie has to run for her life!

Cats don't give a crap whether Winnie is there or not.