Shore Leave

Enterprise visits an idyllic planet, where McCoy encounters a large white rabbit that is "very late". And shortly afterwards, a little girl who is following him. McCoy isn't becoming insane; it soon becomes apparent that thinking about a thing will cause it to materialize, as everyone encounters people and things from their past or their fantasies. But something on the planet's surface is draining power from Enterprise. And then McCoy, convinced that what he sees is a harmless illusion, confronts a charging knight - and dies, pierced through the heart! What kind of odd world is this, and how can the ship and crew escape it?