The sixth book in The Wheel of Time is without a doubt, the turning point in the series (and probably the longest book as well). It's where all innocence is lost, all bonds are broken, and "the world is changed forever."
Mazrim Taim, the false Dragon, is brought before Rand al'Thor. Rand gives him a task, something that has never been done before in this Age and something nobody would have ever expected.
Egwene is summoned away from the Wise Ones she is with, and must accept a new role which she is not sure she's ready for.
Perrin also, feels the pull of ta'veren, and has to make a choice of where to go.
Everything in this book builds up to a climatic ending that changes every aspect of the story. The ending is considered by many to be Jordan's best moment in the series.