Every morning, the phone in our home rings promptly at 9.

“Hello, Carolyn,” my 80-year-old mother will say, picking it up after less than one ring. She knows, instinctively, as she has for the last decade, that her best friend from kindergarten is on the other end of the line.

Their daily ritual began a few years ago, when Carolyn, now 81, started spending the winter in Florida. It was an easy way for them to keep in touch when they were not in the same Michigan town they have both lived in since college.

As they grew older, it became a way to check up on each other’s health every 24 hours, particularly as Carolyn, a widow, lived alone and had a heart ailment. It was their lifeline, literally, as they had shared their entire existence together since age 5, and they were not about to break the bond now just because it was harder for them to shuttle back and forth to each other’s homes.

But three weeks ago, when my mother called her at 9 on a Sunday morning (the ritual being that Carolyn calls on weekdays, my mother on weekends), Carolyn did not pick up.

I was at a baby shower for the daughter of one of my oldest friends, ignoring the vibrations in my purse as I gurgled with her girls over teeny socks and high-tech strollers. But when I finally looked down at my cellphone and saw two missed calls — one from Carolyn’s daughter, who lives in Massachusetts, and the other from Carolyn’s niece, who lives a mile from us — I ran outside, leaving a celebration about life for what I imagined would be a discussion about death.

The good news was, Carolyn was still alive and being well cared for in a hospital, though weak with a severe chest infection. The bad news was, her prognosis was dire, and I had to be the one to tell my mother, who had not yet been reached.

My parents have become more than accustomed to losing close friends in recent years. In fact, I often know they have lost another in their group only when they suddenly appear in the kitchen, dressed in dark clothing.

“Who is it this time?” I will ask gently. But until this past year, when my parents lost two other close family friends, it was rarely anyone I was in touch with on a daily basis.

Carolyn was different. She has always been a large part of my life. I grew up alongside her children, not just during the school year but also every summer. Our lake cottages were a five-minute bike ride apart.

Even when I later moved 6,000 miles away to Egypt, Carolyn visited me with my parents. Though what I always remember best is the time she came to visit me when I was in my early 20s. She stopped by, only to find my mom and dad gone and my boyfriend and me there, by ourselves. She never said a word to my folks until I married him.

Nor did she tell them when she caught me smoking cigarettes in high school or learned I was about to be kicked out of my college sorority as the revered local alumni contact.

My mother took the news well when told that Carolyn was in the hospital, but what none of us could handle was the phone not ringing at 9 a.m. during the long week afterward when she had a tube down her throat and could not talk.

And then, when she could finally speak, none of us liked what she had to say. She was refusing treatment and called to say goodbye to all of us, one by one, including my son, Charles, a senior in high school, who had become a particular favorite of hers since we moved back.

“I’m off to heaven,” she told him in a matter-of-fact tone, offering to pray for the University of Michigan football team, which this season could certainly use some help from on high.

“We are going to have to find another way to communicate than the phone when I am gone,” she said to my mother. Carolyn did not want my mother to make the long trip down to Florida. With her children and granddaughter now at her hospital bedside, my mother followed her wishes.

I left the room. I could not bear to hear my mother saying goodbye to her BFF of 70-some years.

But then, a week later, when Carolyn learned she could move home with hospice care, everything changed. “I want you to come down,” she said to my mother. “I want to see you again before I die.

Now it was time for me to be worried about my mother: sending her on her own to have a final play date with her bestie had its own set of issues, one of them involving sending a largely sedentary elderly woman off on a plane trip, especially one that would involve her having to change planes along the way.

“Can your mother drive while she is down here,” Carolyn’s daughter Andrea texted me, “or is that a bad idea?”

“Bad idea,” I texted back quickly.

I could see we were going to have to maneuver this mom handoff via text messages. I now regretted letting my husband, Daniel, cancel my mother’s cellphone because she had only averaged about one call every other month. Now she was going to be incommunicado. I wondered if I should be going with her, but Carolyn had requested my mom, not me, at her bedside.

The next morning, my father drove my mother and a very large rolling bag to the Detroit airport. When he arrived home, we sat together nervously for the next five hours, tracking her flight. When a text message finally came through from Andrea saying she had my mother, we both breathed a sigh of relief. The blackout period had been as tense for us as waiting to hear that the Apollo 13 crew had touched down safely.

With her best friend now there and her infection healing, Carolyn began eating and drinking small amounts. After a week, when Carolyn no longer seemed on the brink of death but just extremely tired, my mother returned home.

And then the next day, the phone rang promptly at 9 a.m.

“Hello, Carolyn,” my mother said excited, immediately filling in her childhood friend on the details of all that had happened in Michigan during her absence (not much, if you had asked me).

Five minutes later, aware that Carolyn tired quickly, she ended the conversation, signing off with: “O.K., sweetie. I’ll talk to you tomorrow.”