One Night in Karazhan is Hearthstone's fourth adventure.

The adventure features 13 bosses, spread across four wings (plus a free introductory encounter), as well as a more challenging Heroic mode, and 9 Class Challenges. The adventure features 45 new collectible cards, as well as a new battlefield and 2 new card backs. One Night in Karazhan sees players return to the reimagined glory days of the mystical tower of Karazhan, when a young Medivh was not only the Guardian of Azeroth, but also its most eligible bachelor. After earning the admiration of all through foiling the schemes of the fiendish Arch-Thief Rafaam, emerging triumphant from the Grand Tournament, and resisting even the whispers of the Old Gods themselves, the player is invited to a magical one night-only party that is sure to be talked about for centuries. However, upon arriving, the player finds Medivh missing, and the tower's magical enchantments run amok, turning delightful tricks into deadly traps. It's up to the player to find Medivh, restore order to the crazed tower, and save the day - just in time for the tower's big night.