The time has come once again for Barry Allen and Oliver Queen to work together to save the world!

The upcoming two-episode crossover event for 'The Flash' and 'Arrow' has a new extended trailer showing the two superheroes teaming up to protect Kendra Saunders (Ciara Renée), who turns out to be the reincarnation of a powerful ancient princess.

The extended crossover trailer opens with Oliver Queen (Stephen Amell) proposing a toast on his reunion with Barry Allen (Grant Gustin), although he adds, "I wish it wasn't just the dark times that brought us together." It is revealed that the two heroes have decided to work together to find Vandal Savage (Casper Crump), who Barry describes as "an immortal madman on a rampage against a reincarnated warrior princess." Cisco (Carlos Valdes) still manages to lighten the mood by asking, "Since when did our lives suddenly turn into an 'Indiana Jones' movie?"

The trailer also shows more footage of Kendra finding out about her past life through Carter Hall (Falk Henstchel) as well as her training to become Hawkgirl, and it becomes clear that she doesn't necessarily agree with Hawkman in the way he treats her friends. There are more action sequences, including Barry Allen saving Cisco and Kendra, Black Canary (Katie Cassidy) making use of the Canary Cry and Oliver Queen taking on Vandal Savage.

The two-episode crossover event will start with the episode 'Legends of Today' of 'The Flash' then followed by the 'Arrow' episode titled 'Legends of Yesterday.' The titles of the episodes are a reference to the upcoming CW spin-off TV series 'Legends of Tomorrow,' which will star Ciara Renée and Falk Hentschel as well as former 'Arrow' star Caity Lotz.

'Legends of Today' will air on The CW on December 1 while 'Legends of Yesterday' will premiere on December 2.