Set in an alternate history where masked vigilantes are treated as outlaws, Watchmen embraces the nostalgia of the original groundbreaking graphic novel of the same name, while attempting to break new ground of its own.
 
This series is a continuation of the 1986 graphic novel instead of the 2009 movie adaptation.  Many story events and characters from the graphic novel that were changed or removed in the movie are mentioned or shown in the series.  Most notable difference being the Squid Attack on New York, which was completely changed in the 2009 film, so it might be a good idea for you to read the graphic novel before watching this amazing show.
 
FUN FACT:  This is actually the second attempt at a Watchmen TV series. Terry Gilliam attempted an adaptation in the early 90s but could only conceive the story being so epic that the time it would take could only be accomplished on television rather than film. Gilliam's vision went into pre-production with HBO & cast Robin Williams as Rorschach, Jamie Lee Curtis as Silk Spectre, Gary Busey as The Comedian, & Kevin Costner as Nite Owl. The project ultimately dissolved after HBO failed to provide a large enough budget for Gilliam's vision. Gilliam himself later claimed afterwards that an adaptation would've been "unfilmable" anyway.