User blog comment:Darkcloud1111/''The Mark of Athena'' Plot Holes/@comment-3146930-20121014230006

Here is one that may not be a plot hole, just an oddity. So all during The Son of Neptune, the Doors of Death are described as Thanatos' personal way in and out of the Underworld. However we find out in The Mark of Athena that the doors in the Underworld are in Tartarus, a place that Thanatos never goes to (or even the gods for that matter). Also, if the doors are in Tartarus, how did Echo and Narcissus use them to escape. They weren't enemies of the gods (well Echo did refuse Pan, but I don't think that deserved Tartarus), so how did they use them to escape? Did they jump into Tartarus from the Underworld and then walk out using the doors? On that note, Thanatos said the doors weren't in a physical place and could only be found through questing, yet in The Mark of Athena, we find out exactly where the doors are, a physical place called the House of Hades. The Doors of Death seem to be one big plot hole...