Thirty books into her Stephanie Plum series, Janet Evanovich has her writing process down. She maintains two steno pads for each novel, including her latest. One, she explained in a phone interview, is where she keeps track of what her characters are up to — the pickles she wrote them into that day, how they’ll emerge when she gets back to work in the morning. The other notebook is filled with information about the trouble-attracting, doughnut-loving cast who fall in and out of love and drive like maniacs between the covers of Evanovich’s books. This is the ledger she returns to time and again, to make sure her story is consistent.

“I have about 60 pads for the Plums,” Evanovich said. (She has several other series going at any time, including the Gabriela Rose novels and the Fox and O’Hare books.) “Some of them have gotten lost in the many moves that I’ve made over the last 30 years. The earlier ones are packed away in cardboard boxes somewhere in my attic. But my method has remained the same.”

But the steno system is not an exact science, Evanovich admitted. (Originally from South River, N.J., now based primarily in Naples, Fla., she holds onto both the accent and dry humor of her home state.) For instance, Stephanie Plum’s boyfriend, Joe Morelli, used to have a scar on his eyebrow. From book to book, it migrated from, say, the left side of his face to the right. Evanovich’s eagle-eyed readers quickly spotted the inconsistency — and now, she said, “I don’t talk about the scar anymore.”

The same approach applies to Plum’s sister Valerie: “She kept having kids and, after a while, I couldn’t keep track of the kids, so I had to get rid of Valerie.”

Evanovich said, “The fans are amazing! They remember everything; I remember nothing. They’ll come to signings and they’ll be talking about characters and I’ll be just totally embarrassed because I have no clue.”

Nevertheless, she continues to write books at a dizzying clip — the deadline for the next Gabriela Rose novel is Feb. 15 — and “Dirty Thirty” debuted at No. 1 on the hardcover fiction list. The milestone volume has a few celebratory touches, including chapter breaks festooned with diminishing stacks of doughnuts and endpapers featuring the many bookplates Evanovich has signed over the course of the series.

At the back of the book, readers will find 30 favorite quotes culled from Plum’s many adventures. In No. 22, the bounty hunter neatly sums up her own indestructibility: “I’ve been run over by a van, stun-gunned at least twice, injected with some sort of narcotic, and there’s a good chance I’ve got bubonic plague. Today isn’t a good day.” Spoiler: She bounces back.

Elisabeth Egan is an editor at the Book Review and the author of “A Window Opens.”