Collects Original Sin: Thor & Loki #1-5 (Original Sin #5.1-5.5).

Thanks to the events of ORIGINAL SIN, the deepest secret of the Nine Realms has been revealed: namely, the existence of a Tenth Realm! Now, Thor and Loki must embark on a quest to find this strange new world - and to discover the sister Thor never knew he had: the Guardian of the Galaxy known as Angela! But can Loki be trusted? What is the startling secret of the Tenth Realm? And will brother and sister murder each other before the truth comes out?