Since 2009, Roz Chast’s parents had resided in her closet. To be more precise, their cremains — housed in bags inside boxes — had cohabited with her shoes, clothes, wrapping paper and the rest of the miscellany we sometimes call clutter. This final detail of Chast’s best-selling 2014 book, “Can’t We Talk About Something More Pleasant?,” has inspired many readers to send her empathetic notes — it turns out Chast isn’t the only one whose late parents are in the closet — but none sparked the New Yorker cartoonist to move her family from their wardrobe tomb.

(Courtesy of Bloomsbury Publishing)

Until one day last year when Chast received a message through her author website — mail she checks rarely — and found a curious note.

It wasn’t about Chast’s parents per se, but about another detail in the book: Chast’s older sister, who was born prematurely and died one day after her birth, in 1942. Chast was born 12 years later, and her sister became part of hushed family lore, never to be discussed.

Chast’s reader wanted to discuss it.“There was a mystery that needed to be solved,” the letter said in part, and the reader had some clues. She said she had information about Chast’s sister’s grave.

“I did find it interesting,” Chast wrote in a two-page cartoon in the July 25 issue of the New Yorker. In the piece, Chast explained how, using the site findagrave.com, Chast not only located her sister’s unmarked grave at a cemetery in Queens but found that the only available mausoleum niche there was spot J-2, an eerie reversal of the number of her parents’ longtime apartment, 2-J.

“If you put a detail like that in a short story,” Chast said in a phone interview, “someone would be like, ‘That’s really cornball — you gotta take that out.’ ”

But it was just the nudge Chast needed to clean out her closet (to use another cornball phrase). This spring, she loaded her parents’ ashes into a bag and took them — via subway and bus — to their new home in J-2, which also happened to have a view of her sister’s grave. “It was time to say good-bye,” Chast writes.

On the phone, Chast talked about this unexpected twist to her story.

(Courtesy of the New Yorker)

Q. Tell us about the day you discovered your sister.

I was visiting my daughter in Portland, Maine. The plane landed, and I pulled out my phone and saw I had gotten email from the guy [from the cemetery she had written to] that said “I believe I found your sister.” That knocked me backwards. I have always been an only child. [The man from the cemetery and I] corresponded a bit. I went out there. He showed me the book of records — archives, maps. In the back of my mind, I’m thinking, “This is getting to be such a weird story — I might want to write this up.” We found her gravesite. And it turned out my mother’s parents were there, also.

My sister’s grave was unmarked. My mother nearly died giving birth to her. Back then, it was common in such cases for a rabbi to take care of everything because it was so upsetting. My sister had no name, as far as I know. My parents didn’t want to talk about it. My mother would refer to it as “that mess.”

New Yorker cartoonist Roz Chast (Bill Franzen)

Q. Have you had further contact with the reader who sent the email that led to your sister?

I did write to her. I told her I was writing it up and that the New Yorker had bought it. I thanked her like every other word — very sincerely. Without her having written, my parents would probably still be in my closet.

Q. Are you going to update your book?

No, I’m leaving the book as is.

Q. So has this brought you closure, if there is such a thing?

When I turned over the boxes to this guy and he climbed up the ladder [to the niche], it definitely felt more final than having my parents in my closet. I don’t know why, but it did.

Q. How much time are you spending these days on findagrave.com?

I know! It’s like lost bank accounts. But I haven’t been back. I haven’t thought of any other people to look up.

Q. And what about the newfound space in your closet?

Well, you know how space in closets fills up with other things . . . boxes, an iron — stuff.

Q. Are you checking email more regularly now?

Yes! You never know — someone else could have some interesting piece of information. Did you know you have a twin sister living in Tokyo that your parents never told you about? That’s what every person hopes — that there’s some secret that you didn’t know about your parents or your family. But so far so good.

(This interview has been edited and condensed for clarity.)

Nora Krug  is an editor and writer for Book World.

Roz Chast’s cartoons are on exhibit at the Museum of the City of New York through Oct. 9.