It was more than 20 years ago, back in 1990, that a first generation of fans got acquainted with Janie Johnson. Moved by seeing an airport wall filled with homemade missing-child posters, Cooney wrote The Face on the Milk Carton, the story of a teenager who sees a photograph of her three-year-old self and realizes that the doting parents she’s always known aren’t the family she was born to. PW’s review cited the novel’s “strong characterizations and suspenseful, impeccably paced action, calling Janie’s emotional roller-coaster ride “both absorbing and convincing." January brings the fifth and final volume of Caroline B. Cooney’s Janie series, Janie Face to Face (Delacorte). (Warning: spoilers ahead.)

Though Cooney considered The Face on the Milk Carton a standalone novel, her readers had other ideas. “I never thought of it being a series at all, but kids would write, and they would say ‘whatever happened to Janie?’ ” says Cooney. Sparked by these persistent questions, Cooney and Beverly Horowitz, her longtime editor at Delacorte, began hashing out Janie’s next steps. This was the genesis of the second book in the series, released in 1993 and titled – of course – Whatever Happened to Janie? Three years later, in 1996, came The Voice on the Radio, followed by What Janie Found, published in 2000. “None of this was planned, but time would go by and another idea would just pop up,” Cooney says.

Fast forward to the current decade, when Horowitz revisited the books while preparing them to be reissued as Random House trade paperbacks in May 2012. “I was repackaging the books, and in working on the repackage, I said to Caroline, ‘Gee, whatever happened to Janie and Reeve? By now they’d be in college,’ ” Horowitz recalls. “She said, ‘I’m finished with that.’ And then a few weeks later she called me and said, ‘Oh my goodness, I’m not finished with them.’ ” Horowitz proposed Cooney write a short story, to be available only on digital reading devices, that would bring readers up to date with Janie’s life.

In order to immerse herself once again in Janie’s world, Cooney took on the task of writing something about every single character that had appeared in the series. “I didn’t know how to get at a book about Janie and Reeve when they were older,” Cooney says. To create a fully realized portrayal of her central characters, Cooney revisited the entire cast, including Janie’s classmates and younger brothers, and visualized how each character would have developed over the years. “I had to read each book very carefully for clues,” the author recalls.

Not only did Cooney have enough for a short story – the e-reader exclusive What Janie Saw was released in May 2012 to accompany the new editions of the first four books – her explorations had uncovered so much new material that she couldn't resist starting a fifth novel.

Set mostly during Janie’s sophomore year of college, Janie Face to Face chronicles the rekindling of the romance between Janie and her one-time boyfriend Reeve, who has embarked on the first year of what looks to be a dream career. For Horowitz, having two familiar characters reach the cusp of adulthood is an element that will likely expand the novel’s readership. “I do feel there is a bunch of kids who are now in their twenties who can relate to Janie in college and Reeve in the work world,” said Horowitz. “And there is also an [older] adult reader, because what happened to all those parents [in the novel]? The new reader, the nostalgia reader, and that new crossover person – I’m hopeful that it will appeal across those areas.”

Of course, a happy ending on its own simply isn’t enough to resolve a story as complicated as Janie’s. Certainly not while Janie’s kidnapper – the sinister yet pathetic Hannah Javensen – is still on the loose. So even as Janie and Reeve speed toward their happy ending, Hannah moves ahead with her own twisted, vengeful scheme against Janie and the people she loves.

Readers who have wondered about Hannah, her backstory, and her motivations, will find Face to Face fills in many, but not all, of the blank spaces. Even for her creator, the novels’ villain had remained something of a mystery. “I had not thought about [Hannah] in the previous years. All that had to be decided,” said Cooney. “It was sad because you knew whatever her story was, it was tragic and it was rotten.”

Portraying the ever-evolving technology of the past couple of decades was another challenge for Cooney. Though only five or six years pass in Janie and Reeve’s world, communication tools and entertainment media have changed immensely since The Face on the Milk Carton was first published. When Janie’s story starts, her bedroom accessories include a collection of cassette tapes. By the time of The Voice on the Radio, Janie emails Reeve via her AOL account, and in Face to Face, her decisive use of her cellphone camera helps bring Hannah to justice.

For Cooney and Horowitz, the answer was to keep each book’s technology true to the era in which it was written. “Obviously I’ve done a huge time lapse but this is fiction and my readers are brilliant,” says Cooney. “I think kids will take it in stride just like they take technology changes in stride in their own lives.”

Despite this laissez-faire attitude, readers may notice that it is Facebook oversharing that enables Hannah to track her quarry. Besides being a convenient way to move the plot along, this was a good opportunity to make a point about privacy, Cooney says: “Maybe a tiny bit of me was being a bit parental, saying, ‘You do realize, once you put this stuff on your page, anyone can see it.’ It may be just a speck of a warning.”

With Hannah permanently vanquished and Janie and Reeve together forever, could there possibly be another sequel? The answer is a firm “no,” from both Cooney and Horowitz. When asked how it feels to have wrapped up the final volume of the Janie books, Cooney replies, “It was so satisfying. I don’t think I’ve ever enjoyed a writing project more. Though I say that about every project,” says Cooney. “All the books were about good people who had to compromise terribly to make the right choices. Here finally was a chance to write a book where good would triumph. I do believe in happily ever after even though it’s not fashionable right now.”

And how does Horowitz feel about saying goodbye to a cast of characters she’s worked with for more than 20 years? “I’m happy to know all I know about Janie and all these characters and then I’m going to just hope they’ve been sent in the right direction and life is good to them. And I think that’s fine, and I’m OK with it,” Horowitz says. “As an editor, you get used to that. Because most books end and you don’t get a companion or sequel.”

With Janie Face to Face due out next month, Cooney has moved on to her next project, a novel about the children who sailed to North America on the Mayflower. “I’m writing a story that starts in 1607 about the first attempt that the Pilgrims made to escape England,” Cooney explained. “I’m in love with all my Pilgrims.... It’s the greatest adventure in American history and I want it to be as exciting as it really was.”

Janie Face to Face by Caroline B. Cooney. Delacorte, $17.99 Jan. 2013 ISBN 978-0-385-74206-1