I forget how I knew about this book -- another one I bought with that gift card. The author is the woman who wrote Pay It Forward.
Here's the summary:
While duck hunting one morning, childless, middle-aged Nathan McCann finds a
newborn abandoned in the woods. To his shock, the child—wrapped in a sweater and
wearing a tiny knitted hat—is still alive. To his wife’s shock, Nathan wants to
adopt the boy…but the child’s grandmother steps in. Nathan makes her promise,
however, that one day she’ll bring the boy to meet him so he can reveal that he
was the one who rescued him.
Fifteen years later, the widowered Nathan discovers the child abandoned once
again—this time at his doorstep. Named Nat, the teenager has grown into a sullen
delinquent whose grandmother can no longer tolerate him. Nathan agrees to care
for Nat, and the two engage in a battle of wills that spans years. Still, the
older man repeatedly assures the youngster that, unlike the rest of the world,
he will never abandon him—not even when Nat suffers a trauma that changes both
of their lives forever.