Before embarking on this quest, it is recommended that you have a weapon that does shock damage, armor that has shock resistance, and potions of resist shock. These are vital for dealing with the Undead Dragon.
As you start, you will have to cross a wooden bridge where you will encounter Belegond and Aerwaen, they will tell you that necromancers are indeed at the shrine of Mara. After speaking to them, continue on and you will have to deal with a forest spider, once defeated, continue on where you will encounter a wisp and a wispmother.
Just after this, you will have to fight a spriggan earth mother that is guarding the Varla Stone of Frost, once you collect it, retrace your steps and continue down the other path.
Down this other path there are three forest trolls in a clearing, once they are dealt with, you will then have to fight a giant forest spider and a forest spider. Just after these spiders are a pair of skeleton knights and the undead Dragon, as stated before, shock attacks to drain the dragon's magicka are vital so that it cannot bombard you with shouts, drink a shock resistance potion as well to lessen the shock damage the Dragon does.