The enemies of Oliver Queen (Stephen Amell) are on the move to take control of the city in the upcoming episode of "Arrow" season 6. In episode 18, titled "The Dragon," Ricardo Diaz (guest star Kirk Acevedo) is determined to gain more power and influence, as he aims to bring down the current mayor of Star City. His quest for power will bring him closer to underground syndicates. Meanwhile, Oliver is still reeling from the exit of his best pal, Diggle (David Ramsey) from his team, although the hero must remain strong in the face of new threats in town.

According to the official synopsis for "Arrow" season 6 episode 19, Diaz is scheduled to meet with a powerful underground circle in the country called The Quadrant. With the help of Laurel Lance/Black Canary (Katie Cassidy), Diaz will try to convince the group of mafia families to join his cause as he aims to take over all operations inside Star City.

It looks like The Quadrant is the best option for Diaz to ask help, given that the groups inside the coalition are in charge of the biggest organized crime activities in the United States. 

Of course, The Quadrant's answer to Diaz's proposal is not yet set in stone, and anything could still happen from this point onwards. On the other hand, Felicity (Emily Bett-Rickards) will be working with Curtis (Echo Kellum) to build the Helix Dynamics. Felicity has decided to finish the Helix following Oliver's recent decision.

There might be a little problem down the road, however, given the shake-up in Team Arrow. Curtis made an action that has affected the group, most especially Diggle, but Felicity must overcome all distractions to deliver their latest project on time.

The promo trailer for "Arrow" season 6 episode 19 has a preview of Oliver and Felicity sharing a romantic moment together as the former reveals his decision. Whatever that may be, it looks like Felicity is willing to accept that decision, no matter what the cost is. 

"Arrow" season 6 episode 19 will air this Thursday, April 19, at 9 p.m. ET on The CW.