They call themselves "Dumbledore's Army," in reference to Harry Potter and his friends who battle the "Dark Arts."
Their mission: to translate the moral lessons of the "Harry Potter" novels into real-world action. But instead of using wands and witchcraft to combat sinister forces, they channel online social networks to fight earthly evils such as poverty, illiteracy and human-rights abuses.
As fans gear up for "Harry Potter and the Deathly Hallows -- Part 2," the final installment of the blockbuster movie series, members of the nonprofit Harry Potter Alliance predict that a trail of good deeds and charity will linger far after the last spell is cast.
"It is a great way to blend people's desire to make the world a better place ... with Harry Potter fandom," said Katie Twyman, a student at Normandale Community College in Bloomington, Minn., who works for the national Potter Alliance and heads the state's chapter.
"A lot of people read the books and they're left wanting to do something more."
The Boston-based alliance gives those fans direction for pointing their wands.
This year, for example, it encouraged its roughly 80 national chapters to join its "Deathly Hallows Campaign" tackling global warming, illiteracy, bullying, depression and more.
The campaign includes efforts to convince Warner Bros. studio -- which owns the rights to the "Harry Potter" films -- that all "Harry Potter"-themed chocolate should be fair-trade certified, meaning that cocoa farmers were paid fair wages and no child labor was used.
Their activism has caught the attention of "Potter" author J.K. Rowling, who once worked for Amnesty International. She had praised the alliance for its work calling attention to genocide in Darfur in 2007.
Last year, she donated several autographed books for the alliance's Haiti fundraiser -- which raised $123,000 and had cargo planes named after the book's characters.
Her thank-you note, posted on the alliance's website, says: "You cannot imagine how awed, moved and humbled I am to know that planes named Harry, Ron and Hermione are going to be flying off to help."
Jennifer Dorsey, a spokeswoman for the national alliance, has no doubt that even more folks will join the alliance after the franchise's last installment leaves the screens. "We've learned that fans care about the books in so many ways," she said.
Twyman, 19, is typical of members -- young, enthusiastic, media-savvy.
She stumbled across the alliance while surfing "Potter" websites. She and a friend started a Minnesota chapter 18 months ago while still in high school.
It's a small group still finding its way. Members collected about 2,000 books for the alliance's literacy drive. They also get involved in national campaigns.
They held a "Wizard Rock" concert last month, a local version of the national events featuring musicians who support the "Potter" alliance campaigns with their websites and online concerts.
Twyman said the concert in her backyard (in this case, a one-man show) drew about 50 people, and nearly 200 more watched it streamed live online.
Twyman also blogs for the national alliance, most recently for its "body image" campaign, sharing her own story about depression.
"This has changed my life," said Twyman, whose bedroom is filled with "Harry Potter" posters and banners. "It's introduced me to all sorts of new people. It's uplifting to know you're changing people's lives."
Meanwhile, University of Minnesota student Kelly Adams, 19, is recruiting members for a chapter at the school. She's a member of the university's "quidditch team" -- quidditch being a fictional sport played on flying broomsticks in the "Potter" series.
She wants the group to be both active in online national campaigns and to create a real-world space where members can just hang out and socialize.
The alliance, she believes, could attract an untapped pool of activists.
"It can be unappealing for some people to do charity work," Adams said. "This way we can always talk about Harry Potter if we get bored."
The alliance was formed in 2005 by Andrew Slack, a then-Brandeis University student who is now executive director, and Paul DeGeorge, a singer in the Harry and the Potters band.
Unlike traditional nonprofits, it relies on blogs, online petitions and contests, tweets, livestreaming events and other social media to spread its message.
In the vast scheme of national nonprofits, the alliance's effect has been small and scattered.
But its organizing model has caught the attention of veteran activists such as Cara Letofsky of Minneapolis.
She recently joined the alliance after learning about work defending gay marriage.
"It's an under-the-radar, 21st-century way of organizing people -- the idea that you can motivate people to do good through books," said Letofsky, a former policy aide to Minneapolis Mayor R.T. Rybak and founder of City of Lakes Community Land Trust.
"It's one that people like me can learn from."