Mary is the woman John Watson chose to marry. She helped John cope after Sherlock's fake death, though she later revealed a secret past as an assassin by shooting Sherlock. Despite this, John chose to stay with Mary, as he understood her fears and saw the good in her, just as he understood and accepted Sherlock's flaws. Mary's lifestyle was similar to Sherlock and John's in that they all craved the thrill of the chase, bonding them together beyond Mary's lies and shooting of Sherlock.