The CW has released the official synopsis for the episode, which you can read below.
THE POWER WITHIN — When Mallus’ power over Sara (Caity Lotz) resurfaces, she unwittingly becomes the bearer of one of the Totems. Rory (Dominic Purcell) must conquer his dark side in order to wield his own Totem power to help save the crew. Meanwhile, Agent Sharpe (guest star Jes Macallan) notices that something is wrong and recruits someone unorthodox to help.
Brandon Routh, Nick Zano, Maise Richardson-Sellers, Keiynan Lonsdale and Nick Zano also star.
April Mullen directed the episode written by Grainne Godfree & Morgan Faust.
Ryan first played the role of Constantine on a self-titled NBC series, which lasted for one year. After that, he appeared in a Sara Lance (Caity Lotz)-centric episode of Arrow, officially bringing the character into The CW's shared DC Universe. Ryan followed this by portraying Constantine in the animated feature film Justice League Dark, and will follow up his Legends appearances with a Constantine animated series for CW Seed.
"I don't know if I've ever seen an actor so completely bring to life an established comic book character as Matt Ryan did for John Constantine," Constantine showrunner Daniel Cerone told ComicBook.com. "Between the NBC series and his subsequent appearances on CW, it would feel strange to see or hear anyone else in that role at this point."
DC's Legends of Tomorrow airs on Monday nights at 8 p.m. ET/PT on The CW. "Necromancing the Stone" will premiere on March 19.