Can a man be a witch? Can a woman be a wizard? Where are the boundary lines drawn? What defines what? What is simply tradition and what is a hard in stone rule? Most would tell you that only women can be witches, only men can be wizards, and that these are hard and fast rules. Until a dying wizard accidentally passes his powers (and staff) onto the baby that he thinks is the eight son of an eight son. Only the baby is a girl.
"Equal Rites" is about that baby girl, Esk, and her attempt to fumble her way through her magical legacy. Fortunately she's not entirely on her own, Granny Weatherwax, a local witch, takes on the task of watching over Esk and trying to direct her magic. She trains Esk up as a witch, a lot of it is just headology anyway, but the magic has other ideas.
Eventually it becomes obvious that the magic Esk inherited is not simply content to let her be a witch. No one knows what to do with a woman wizard, but everyone figures that the only one's who will be able to figure it out are the wizards of the Unseen University.
Getting to the University is going to be quite the journey though, and once Esk gets there she faces a bunch of men who are VERY set in there ways.