According to the product description, the expansion will send Guardians on a journey to Mercury where they will explore the mysterious Infinite Forest. The expansion will include new story missions and adventures; themed weapons, armor and gear; new cooperative activities; new competitive multiplayer arenas; and more.
The official expansion description reads:
“Destiny 2 Expansion I: Curse of Osiris continues your Guardian’s journey with all-new story missions and adventures set in a new destination, Mercury. Journey through time and space to learn the secrets of Osiris, avert a dark future, and rebuild the ties between the legendary Warlock and his greatest student – Ikora Rey.”
Kotaku says The Curse of Osiris will release in December.