How to kill superheroes? Go back to a time when they are still vulnerable, of course.

That's just what the preview storyline promises when "Legends of Tomorrow" returns.

The synopsis for "Legends of Tomorrow" episode 12 offers a lot of preview. It says:

"The team is targeted by The Pilgrim (guest star Faye Kingslee), a deadly assassin who wants to erase the Legends from the timeline by killing their younger, non-superhero selves. As a protective countermeasure, Rip (Arthur Darvill) decides Sara (Caity Lotz), Snart (Wentworth Miller), Rory (Dominic Purcell), Professor Stein (Victor Garber) and Jax (Franz Drameh) need to kidnap their past selves first before The Pilgrim gets to them.

"Coming face-to-face with the younger versions of themselves proves to be both a physical and emotional challenge for certain members of the team who would rather forget their past. Rip tells them he has a refuge for their precious cargo - an orphanage that raises future Time Masters and where he himself grew up."

But it's not as simple as going back in time because their younger selves grew up in different timeline, so it would be interesting how the show will address that bit of a kink.

"How much will they have changed if they all grew up in a different time period altogether?" wondered Cartermatt. "Tricky as it may be, they will all figure out ways to go back and restore the timeline. This would all get really messy otherwise."

Watch out for more preview of "Legends of Tomorrow" as episode 12 airs on Thursday, April 21.