Iris tells Barry that not everyone has RSVP'd for their wedding yet. Oliver and Felicity decide to go, as do the Legends team, all while fighting villains. 

Kara and Alex drink wine and discuss their misery over their relationships. Kara decides to bring Alex to the wedding. 

Cisco and Wells develop a cure for Firestorm. 

Everyone is celebrating at Barry and Iris' rehearsal dinner. Alex and Sara bond over the open bar. 

Barry asks Kara if she would sing. 

Dr. Stein finds a way that Jefferson could still have superpowers and be a legend without Firestorm. 

Joe makes a heartfelt speech and Alex and Sara get drunk and make out. 

Oliver asks Felicity to marry him. She says no, loudly, and everyone hears. 

Kara sings Barry and Iris' song from the musical, "Running Home To You" while Iris walks down the aisle. 

The wedding is interrupted by Nazis. Everyone immediately starts fighting while the guests evacuate. Kara takes on one who has similar abilities to her. She gets the upper hand and the Nazis fall back. 

Cisco is unconscious with a concussion.

They manage to take one of the Nazis hostage and lock him in Star Labs. 

The Nazis are all evil versions of the heroes.