The CW's popular DC series "Arrow" will introduce a new threat to Star City, thus making the remaining members of the original Team Arrow work together and fight the emerging enemy. However, Team Arrow should also be concerned about the relationships within the group, particularly Oliver Queen (Stephen Amell) and John Diggle (David Ramsey).

"Arrow" season 6 episode 17 will see Oliver and Diggle facing a new threat, although it appears that the biggest challenge in the episode is keeping their relationship strong enough. Per the latest synopsis, the upcoming episode titled "Brothers in Arms" could end in a shocking duel between the two best pals.

Oliver and Diggle have been through thick and thin for the past seasons, although it is rumored that the long years of their friendship will come to an end in "Arrow" season 6. It is not known what will come up that will cause a major rift in their relationship. If anything, episode 17 could be the beginning of Diggle's separation from Team Arrow.

Meanwhile, "Arrow" season 6 episode 17 will give an update on Curtis' personal life. The fans have seen Curtis' previous heartbreak as her previous romantic relationship did not work out. This time around, she will exert some effort to make her current relationship last, but unfortunately, her new boyfriend seems to have a problem with vigilante activities in Star City. It will be interesting if Curtis will allow her boyfriend's opposition of vigilantism to affect her own vigilante life.

The episode 17 official plot synopsis states: "Oliver makes a daring move that could cost him everything — Oliver and Diggle face their biggest challenge yet. Curtis (Echo Kellum) is disappointed to find out his new boyfriend has a firm anti-vigilante stance." 

Previously, "Arrow" season 4 welcomed back Nyssa al Ghul (guest star Katrina Law) as she warned Team Arrow about the League of Assassin's rampage.

Episode 17, "Brothers in Arms," will air on April 5 at 9 p.m. EST on the CW.