Rick Remender, Nic Klein, Dean White and Joe Caramagna reach deep into the heart of Steve Rogers to produce a gripping and heart-rending conclusion to "The Iron Nail" in "Captain America" #21. Cap and Ran Shen, the Iron Nail, battle for control of Gungnir, a S.H.I.E.L.D. helicarrier that just so happens to be doing a bang-up job impersonating a Transformer, a thundering monstrosity that is yet another piece of propaganda in Shen's war against the west. Shen is trying to make it appear as though Rogers is responsible for Gungnir's actions, especially as Gungnir stomps through the defenses of Nrovekistan.

Remender has been chipping away at Steve Rogers' sanity and grip on reality since the first issue of this series, when he dropped Rogers into Dimension Z without hope of finding his way home. Since returning to his home dimension, that grip has been challenged even more, with this issue delivering the crushing blow. Remender cracks open Rogers' thoughts, giving the readers a firsthand accounting of what the iconic hero is thinking and wrestling with in the shadow of this monstrous threat.

The Iron Nail is a healthy addition to Captain America's collection of foes, but he is a little too malleable, becoming whatever threat Remender needs him to be in order to pose the greatest challenge to Captain America, from shooting projectiles when Cap is out of range to ripping up floor panels from underneath Cap while Rogers is in a dead sprint.

I'm glad to see Falcon still factors significantly into Cap's life, as the Super Soldier's longtime partner plays a big part in concluding the threat posed in this issue. Maria Hill and Nick Fury also make appearances, shoring up the cast of characters around Rogers and providing ample opportunity for continued tales through the percolating subplots. And Remender makes it quite clear by the end of this issue that Steve Rogers is going to need a strong support network around him in the days and issues to come.

Klein's art is duskier than previous series artist Carlos Pacheco, but it is in the same spirit and packed with nearly the same amount of detail. Klein and colorist Dean White are clearly collaborating throughout "Captain America" #21, as there are many panels where texture appears to have come from both sources. The end result is a lively comic that steps out of any preconceived notion of what a "Captain America" comic book should look like. Letterer Joe Caramagna moves the story across the page and panels through the placement and construction of caption boxes, keeping the words of the issue lean and in fighting shape, giving Klein and White plenty of space to do their thing.

With the conclusion of "The Iron Nail," I am truly at a loss as to what comes next. I did not see Remender ending this story in this manner, and the potential story paths beyond the final page seem daunting. Remender set out to shake things up a bit, and he certainly has. Steve Rogers is definitely going to change in reaction to the developments of "The Iron Nail" -- now, it's up to Remender to show readers what those changes will be.