Barry is thrilled when Oliver, Felicity and Diggle come to Central City to investigate a case involving a deadly boomerang.

The crossover continues on Arrow S03E08 The Brave and the Bold.

When Harrison activates the particle accelerator, the team has no choice but to evacuate the five metahuman prisoners. Unfortunately, with time running out, Barry has no choice but to turn to Captain Cold for help. Meanwhile, Eddie escapes but has some surprising news for Iris.

The Flash is forced to make an impossible choice. With the power out in the city, Team Flash calls upon the Rogue Squad to help as Iris is visited by an old friend. Joe and Cecile work on finding a balance.

As the Red Death wreaks havoc on Central City, Barry and Iris come up with a plan and turn to Cecile for help. Barry is faced with what he thinks was his greatest mistake and the Red Death's greatest success. Khione wants to help Team Flash, but Barry can't risk losing her. Joe gives Barry a much-needed pep talk.