'What do you do when the story changes in midlife? When a tale you have told yourself turns out to be a little untrue, just enough to throw the world off-kilter?" Gail Caldwell asks in her latest memoir, "New Life, No Instructions."

While Caldwell's previous memoir, "Let's Take the Long Way Home," focused on her close friendship with the late writer Caroline Knapp, "New Life, No Instructions" is a more introspective work. Caldwell is a few years past 60 and has suffered the losses of her mother, her father, her best friend, and her loyal Samoyed dog, Clementine, within a six-year span. The landscape is looking pretty bleak.

Enter Caldwell's "rambunctious miracle," Tula, a Samoyed puppy to "rescue a human from an avalanche of grief, demonstrate daily the necessity of the forward march." And so Tula does her duty, and then some, quite possibly to the detriment of Caldwell's already compromised physical limitations.

For there is another presence in Caldwell's memoir, one she has shared a lifetime with: the polio that she contracted as an infant in 1951 but was undiagnosed until she was older. It left her with a slight limp and a fierce determination to enjoy the sports she loves, until shortly after she got Tula and could not ignore her pain any longer.

"The narrative can always turn out to be a different story from what you expected," or so she finds out when, after a 10-year run through the health care maze, she meets an astute doctor who tells her that polio is not the culprit here; the pain is caused by a hip ball rubbed down to the bone that requires surgery. This is both good news and bad news for Caldwell; relief for her relentless pain, but a logistical recovery challenge for a woman who lives alone with a very large dog.

This book lacks the intensity of "Let's Take the Long Way Home," which is unsurprising if one considers the time that has passed. In a way, that is the theme of this new memoir: that one must forge ahead in order to get past the pain. There is also the thrill of hope, as she finds out when her operation lengthens her weak leg in a way that she could have never even dreamed was possible. "God kept throwing me a bone once in a while," she says, "just so I would keep going."

Meganne Fabrega is a member of the National Book Critics Circle.