John Constantine’s time as a leading TV hero is done, but he’s not gone from television entirely. This past summer, it was announced that the chain-smoking occultist would guest star during Arrow Season 4, fulfilling a crossover idea that had been gestating since Constantine was still airing on NBC. We knew that Arrow's creative team had to wait a while just to get the idea of Oliver Queen and Constantine together greenlighted, but as it turns out, they also had to jump through a lot of hoops to get Matt Ryan to reprise his role.
Ryan explained to TV Insider that in order for him to don the trench coat for Arrow this season, there had to be some shifting around in order to accommodate a play he was performing in. As Ryan put it:
They moved heaven and Earth to get me here. I was starting rehearsals for a play [Thérèse Raquin] with Keira Knightley in New York on the first of September. And originally, where the episode sat in the season, I wouldn’t have been able to do it because of my schedule. But everybody just pulled together and moved some things around and really made it work.
Although Constantine’s Arrow episode is the fifth episode of Season 4 (airing on Wednesday, Nov. 4), it’s the fourth episode in the production cycle, so presumably that’s the adjustment the show’s crew made to secure Ryan’s participation. Right now his appearance is being labeled as a “one time only” deal, but depending on how well Constantine is received by Arrow fans (many of whom watched Constantine), maybe the writers will get permission from the top brass to use him again at some point... assuming those reappearances can be coordinated with Ryan's future acting schedule.
Oliver will call on Constantine in “Haunted” to assist with helping the recently-resurrected Sara Lance deal with the demons that have come with her revival. As viewers saw last week, the Sara that came out of the Lazarus Pit was animalistic and savage, a consequence of the Pit being infused with the souls of everyone who has bathed in it. With all other options exhausted, Oliver will recruit Constantine to exorcise Sara’s “demons.”
Ryan also mentioned that Oliver and Constantine aren’t friends, but rather acquaintances that have a past together, and the only reason Constantine has agreed to help Team Arrow is because he owes Oliver a debt. It’s unclear whether we will see the history between the two (perhaps on Lian Yu) in a flashback during that episode or not, but presumably his relationship with Constantine is one of the ways Oliver was familiar with magic before Damien Darhk came to Star City.
New episodes of Arrow air Wednesdays at 8 p.m. EST on The CW.