Mine — Robert R. McCammon

OBSESSION...

Laura Clayborne is a successful journalist with a successful stockbroker husband. But her marriage is foundering and her biological clock is winding down. David, her newborn son, is the only light in her life.

Mary Terrell, alias Mary Terror, is a scarred survivor of the sixties. A former member of the terrorist Storm Front Brigade, she now festers in a world of warped memories and unrelenting rage. Quite simply, Mary Terror is mad. Murderously mad.

AND POSSESSION...

When Mary Terror steals Laura's baby and heads west, killing anyone in her way, Laura realises the only way to stop her is to hunt her down. But the closer she gets to Mary, the more she must think and act like her...