WARNING: The following contains spoilers for The Flash Season 7, Episode 16, "P.O.W.," which aired Tuesday on The CW.
When longtime Arrowverse hero John Diggle was last seen in the final moments of last year's Arrow series finale, the A.R.G.U.S. operative and occasional superhero codenamed Spartan was packing up to move with his family to Metropolis before a meteorite seemingly crashed near him. Upon closer inspection, Diggle learned that the fallen object possessed an unearthly green glow, seemingly confirming fan speculation that the character would eventually join the Green Lantern Corps. And as Diggle reunites with Team Flash in Central City, the hero finds himself at a crossroads as he contends with his cosmic destiny.
With Central City beset by warring Godspeeds, an overwhelmed Barry Allen is relieved to see his old friend Diggle return to lend him support. Still working with A.R.G.U.S. and providing a quick update on how Cisco Ramon is doing with the intelligence agency, Diggle comes armed with cutting edge tech to capture the Godspeeds and learn why they're back in Central City from the year 2049 and fighting amongst themselves. And though Diggle provides much-needed support to Team Flash, it becomes clear that all is not well with the career soldier stemming from his unresolved cosmic incident.
During his entire stay in Central City, Diggle suffers from noticeable debilitating migraines, with Cecile Horton using her empathic powers to sense that there is something greater afoot for Spartan. Even as Team Flash braces for the largest influx of Godspeeds to strike the city ever, targeting the amnesiac August Heart kept at S.T.A.R. Labs, Diggle leaves to finally deal with the strange, green cliffhanger that he's left unaddressed for over a year, setting up the character to finally become one of the mightiest superheroes in the Arrowverse.
Diggle's appearance on The Flash was much more telling than his appearances on Batwoman and Legends of Tomorrow, with the latter having actor David Ramsey portray Diggle's ancestor. Diggle's role on Batwoman was much more subdued than the pivotal one he played on The Flash, rescuing Luke Fox from harm before giving him a pep talk that informed Luke in becoming the superhero Batwing. Similar to The Flash, Diggle visibly suffered from a headache though he quickly dismissed it, with speculation that it may be attributed to a neurological condition he developed during Arrow.
While John Diggle has largely stayed off the radar since the funeral of Oliver Queen, the hero continues to inspire those around him, wherever he appears throughout the Arrowverse. Diggle has one last stop planned for the Arrowverse this season, as the character is set to make a guest-starring appearance on Superman & Lois. Whether Diggle's time in Central City and his decision to proceed with whatever his cosmic destiny may be will inform his appearance on Superman & Lois has yet to be seen, but unresolved issues from Diggle's past are quickly catching up to him.
The Flash stars Grant Gustin, Candice Patton, Jesse L. Martin, Danielle Panabaker, Carlos Valdes and Tom Cavanagh. New episodes air Tuesdays at 8 p.m. ET/PT on The CW.