Consequently, when I fell out, her only recourse was to slap and shake me and hope I came out of it without Narcan — and without having to dial 911. She was good at toeing the line, but heroin was tightening its grip on her, too, or else she may very well have left me behind.

She tried finding humor in the situation.

"I like slapping you almost as much as I like rescuing you," she said once after I woke up to her tear-streaked face. "We've got to stop. I'm not always going to be here to save you."

The overdoses cut both ways.

In August, not long before we decamped for North Dakota, Sarah fixed early one morning when her eyes dropped shut and she fell back onto the pillow. I thought she was just enjoying the rush of the black juice sieving through the blood-brain barrier, but then the transformation came. In an instant, her pale face had turned a ghostly blue, her breathing reduced to shallow gasps.

Because we had detoxed during a 30-day road trip we had returned from only three days earlier, our Narcan was packed away. I spent several painstaking minutes tearing through boxes in the dark, moonless night, but was unable to find it. Paramedics arrived 30 minutes later and administered the lifesaving antidote. Eight hours later we fixed as she got ready for work.