'Arrow' season 5 episode 4 spoilers: Oliver embarks on secret mission for Diggle; Can recruits fight Tobias Church without Green Arrow?

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 Oliver (Stephen Amell) steps in for Diggle (David Ramsey) in the upcoming episode of The CW's hit superhero drama "Arrow" season 5.

Titled "Penance," next week's episode will feature a special mission for the Green Arrow. According to the official synopsis for episode four, Oliver teams up with Lyla (guest star Audrey Marie Anderson) to accomplish a secret mission for Diggle. However, Felicity (Emily Bett Rickards) immediately finds out and ends up disapproving the plan and opting o stay behind. Once the villainous Tobias Church (guest star Chad L. Coleman) launches a deadly attack against the city, Felicity will be forced to decide if she wants to send the recruits out without the Green Arrow to stop him.

In a recent post-mortem interview with Entertainment Weekly, executive producer Marc Guggenheim revealed that it won't be long until Oliver finds out about Felicity's relationship with Detective Malone (Tyler Ritter). "No secrets stay secret on Arrow forever," he said. "Oliver's going to find out about Felicity's boyfriend in 505. Because I'm spoiling that, I'm not going to spoil when Felicity's boyfriend finds out that Felicity is working with Arrow."

According to Guggenheim, fans should look forward to episode 6 the most because it will kick the story into a higher gear as Prometheus makes his presence to the titular hero known. "It's a 23-episode season. This is true for all the shows, especially when you've got a big bad that's being introduced in the first episode," the EP explained. "How do you strike that balance between it becoming the Prometheus show and becoming incredibly repetitive and teasing it out? 506 felt very right to us, because 505 feels like the end of a chapter, as it often is on Arrow. 506 kicks things into another gear."

The fifth season of "Arrow" airs every Wednesday night at 8 p.m. ET on The CW.