Chapter nineteen is a pivotal part of Tuck Everlasting. The Tucks face the Man in the Yellow Suit after he enters their home. He has discovered their secret of immortality and plans on selling the magic water that keeps them from aging. He even says they should join him and intentionally try to kill themselves in order to prove the water's powers and entice people to buy it.
The Tucks protest, not willing to allow the Man to tour them around like some kind of bizarre circus. He then grabs Winnie and tries to take her away, but Mae, holding a shotgun, orders him to release Winnie. The Man says he'll make Winnie drink the water and become a part of his scheme. Mae bashes him over the head with the shotgun, killing him.
I think it would be normal for someone to have mixed feelings witnessing this scene in Tuck Everlasting. The Man in the Yellow Suit is undoubtedly frightening and cruel, but Mae did violently murder someone. Still, the Tucks had grown to love Winnie and would do just about anything to protect her. This scene is a classic case of good versus evil, and the reader probably can't help but root for the Tucks.