'3 Willows,' by Ann Brashares

When a series of books has sold almost 9 million copies in North America and two of those books have been made into movies, coming up with a new and equally successful idea can be tough.

That's the situation in which Ann Brashares seems to have been in when she wrote the kickoff to her new series, "3 Willows: The Sisterhood Grows." As the subtitle indicates, the book is as much a continuation of her hugely successful "The Sisterhood of the Traveling Pants" books as it is a departure.

Like a chef not wanting to mess with a successful recipe, Brashares sticks closely to the formula she concocted for her Sisterhood books in "3 Willows." She follows the individual yet entwined lives of teenage friends as they separate for a summer -- only here, there are three, rather than four, main characters.

In place of rebellious Tibby, beautiful Lena, soulful Carmen and headstrong Bee, Brashares gives us bookish Ama, nerdy Polly and wannabe cool kid Jo.

The girls are 14, two years younger than their Sisterhood counterparts, and their friendship is on shaky ground as they graduate from middle school and prepare to enter South Bethesda High, the same school the Sisterhood girls attended when they decided to take turns with a pair of thrift-store bluejeans that, miraculously, fit each of them perfectly.

In "3 Willows," it's the trio of willow seedlings Ama, Polly and Jo have planted side by side that serves as their metaphoric bond. Unfortunately, neither the metaphor nor the book itself is as strong as "The Sisterhood of the Traveling Pants." Although Brashares' new characters and writing are just as wonderful as their predecessors, she does herself a disservice by shoehorning the dynamic of a faltering friendship into a story designed to be about BFFs.

Ama, Polly and Jo first met in third grade when their parents were late to pick them up from school. Ama is a first-generation African American who aspires to follow in the footsteps of her scholarly older sister. Polly is a borderline anorexic who lives with her alcoholic single mom. Jo is dealing with her brother's death and her parents' separation.

Like the original sisterhood, the girls are each unique, but Brashares doesn't work hard enough to explain what first cemented their friendship or what started to tear them apart.