No. You will need to choose a specific room (series), but you will not be required to lock-in the specific story or adventure within that room.
If you are the first to reserve a session, you will have the option to choose the adventure you wish to play. Once an adventure is chosen, it is locked in and others who join the session will not be able to change the adventure choice. If you sign in as an Epic Adventure Club member but do not choose an adventure at the time of reservation, the next person making the reservation can choose from the adventures that you have not played. Your group will be contacted 24 hours prior to the scheduled session to finalize adventure choice.