“Arrow” Season 4, episode 20 will see Oliver Queen (Stephen Amell) bring a former enemy onto his team in order to help stop a larger threat. The CW

Now that the team on The CW’s “Arrow” knows what their big bad of Season 4 has planned, they’ll need to go to tremendous lengths in order to stop him. As a result, the team will turn to a former, and deeply personal, enemy for help to save Star City in episode 21, “Monument Point.”

In the previous episode of the superhero series, Oliver Queen (Stephen Amell) and his team learned that Damien Darhk (Neal McDonough) had stolen a piece of government technology that will allow him to seize control of the world’s nuclear stockpile. Believing he can rebuild civilization following its destruction, it’s up to the heroes to do whatever is necessary to stop the villain and his “cleansing nuclear fire.”

As featured in a teaser trailer for the upcoming episode, posted below, time is not an ally to Team Arrow. With virtually nothing stopping the magical-powered Darhk, the team learns that they only have 20 hours before he launches his evil Genesis plan and wipes out half the planet. With villains like Danny Brickwell (Vinnie Jones) back on the streets taking advantage of the chaos, the team will need a little extra help.

The occasion calls for another experienced computer hacker, and Felicity (Emily Bett Rickards) realizes that the only one that can truly help them is Noah Kuttler (Tom Amandes). Previously, the group encountered him as the villain The Calculator. However, he quickly revealed himself to be the father of Felicity, desperate to win his daughter’s affection despite his status as a criminal mastermind.

According to the episode’s official plot synopsis from the CW, the inclusion of Kuttler in their master plan prompts Oliver to have an intense and frank conversation with the man who was supposed to be his father-in-law. However, with that relationship over for the time being, there’s no telling what The Calculator will have to say to The Green Arrow, but the synopsis teases that it will leave the hero pretty rattled.

Meanwhile, it seems that the bad guy that’s been working in the background of all the events of Season 4, Malcolm Merlyn (John Barrowman) will meet his recently-captured daughter, Thea (Willa Holland), to try and get her on board with his involvement in Genesis. Sadly, he’s not enough of a relative to Thea for her to betray her team and allow the death of millions of people, so the conversation likely doesn’t go too well for him.

To see how it all plays out, fans of “Arrow” will have to tune in to episode 21 of Season 4 at 8 p.m. EDT on Wednesday to see how the team spends its last 20 hours.