What is the turning point of the story?

What Is the turning point of insurgent

Tris, nobley, sacrificed herself for Caleb. She survived the death serum, but was shot and killed by the one and only idiot David. Tobias, desperately wanting to rid himself of emotional pain, attempted forgetting his whole past by consuming the memory serum. He is stopped by Christina, though, and pushes through life, slowly. Him and his mother, Evelyn, eventually grow back together,