The Flash: 10 best episodes, ranked

5. “Duet” (Season 3, Episode 17)

When Melissa Benoist flew onto our screens on Supergirl, fans immediately began calling for a musical crossover with The Flash. Two “supergleeroes” in the Arrowverse? It was too good an opportunity to miss, especially when the two Glee stars had such incredible bestie chemistry they Barry and Kara first met in the first crossover over on Supergirl.

The stars would align (and come out) for The Flash‘s third season, as a mysterious trip into a whimsical dreamscape orchestrated by Music Meister (played by Glee‘s own Darren Criss) would result in a delightful and charming caper that saw Barry and Kara save fictional versions of their loved ones in the dream, all while exercising their vocal chords in the process. It was all about love, as song healed old wounds, with both Barry and Iris, and Kara and Mon-El, overcoming their issues to find each other again.

These shows are at their best when they are lighthearted and fun, and you won’t find a more appropriate example of that than “Duet”. It was heartfelt, it was nostalgic, it was silly, it was wonderful, and getting the chance to see Gustin and Benoist perform the original song “Super Friend” made it worth the wait.

From Benoist’s beautiful rendition of “Moon River” in the opening, to Gustin’s powerful performance of original “Runnin’ Home To you” (not-to-mention seeing a few Flash, Supergirl, Arrow and Legends of Tomorrow stars belting it out in between), this one didn’t just live up to expectations, it exceeded them.