The past several seasons of The Flash, including its ninth and final season, have been a decidedly mixed bag in regard to quality, with unfulfilling subplots and poor attempts at humor. It is then with great pleasure to report that the final season's ninth's episode, titled, "It's My Party and I'll Die If I Want To" is the best episode the show has had in years, certainly all season. Featuring the return of Arrow star Stephen Amell, reprising his fan-favorite role as Oliver Queen, the episode feels like a fitting dénouement to the Arrowverse and a reminder of the close friendship between Ollie and Barry Allen.

As Barry prepares to celebrate his 30th birthday again, thanks to the youthfully rejuvenating effects of being blasted by a gamma beam, the party is crashed the vengeful super villain Bloodwork. Just as powerful as ever, Bloodwork has plans for the speedsters as he uses his mind control powers to leave Team Flash at his mercy. However, the surprising return of Oliver Queen, despite his heroic sacrifice during "Crisis on Infinite Earths" gives Barry the fighting chance he needs to stop Bloodwork once and for all.

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The Flash Bloodwork (Sendhil Ramamurthy) speaks to Barry (Grant Gustin).

There are several major factors that make "It's My Party and I’ll Cry If I Want To" such a standout episode and a significant cut above The Flash's usual output these days. Longtime series star Danielle Panabaker returns behind the camera to direct the episode, a multi-hyphenate role she's held on multiple occasions in preceding seasons. Another wise decision is keeping the focus squarely on Barry rather than wander into the shaky subplots and character arcs that have overshadowed a lot of the show's later seasons.

Of course, Amell's eagerly anticipated return is the biggest highlight here, and it could've been so easy for Ollie's post-mortem appearance to be a handful of dialog-driven scenes, but The Flash takes full advantage of having the Emerald Archer back. Amell not only gets to revisit his solid on-screen chemistry with Grant Gustin but also with guest star and fellow Arrow alum David Ramsey who appears prominently in the episode. This isn't a sidelined reunion, either -- Amell's Ollie is back in the thick of the action as he takes up the Green Arrow mantle one more time to help an old friend.

The Flash Diggle, Ollie, Barry, and Wally stand together in costume outside

The other big returns, which shouldn't be overlooked by Amell's triumphant guest-starring spot, are past series regulars Keiynan Lonsdale as Wally West and Sendhil Ramamurthy as Bloodwork. Wally had been abruptly written out of the show with plenty of mileage left to explore, so it’s good to see the character return to tap into some of that unused potential while Ramamurthy's Bloodwork was one of the series’ more compelling villains in its later years. Both actors fit seamlessly back into their respective roles and one hopes that Lonsdale’s Wally will continue to play a part in the last handful of episodes for the series.

"It's My Party and I'll Die If I Want To" is a perfect reminder to the sheer joys the Arrowverse is capable of on the eve of its conclusion, and almost feels like a suitable series finale. The episode expands upon the shared universe's send-off, including a payoff that never quite was realized in Arrow's own series finale just over three years ago. Featuring some of the most ambitious action set pieces The Flash has ever seen with genuinely heartfelt moments, Amell and Gustin’s on-screen reunion is certainly not a wasted opportunity.

Developed for television by Greg Berlanti, Andrew Kreisberg and Geoff Johns, The Flash airs Wednesdays at 8 pm ET/PT on The CW, with episodes available to stream the following day on The CW App.