The drama series, which stars Claire Danes and Damian Lewis, centres on a recently returned Marine Sergeant Nicholas Brody (Lewis) who is feared to be plotting an attack on America by CIA agent Carrie Mathison (Danes).
The network announced on Tuesday that Homeland's 60-minute format will be expanded to 90 minutes for its first season finale, due to air on December 18.
"Homeland finds Carrie near-catatonic and confined to bed as events swirl around her. Meanwhile, Brody makes his final preparations for the Vice President's policy summit," Showtime offered as a teaser to the episode in a press release.
"The pieces to a deadly puzzle are falling into place, but even as she springs into action, Carrie may be too late to put it all together. When the crisis finally hits, no-one - not even Carrie - can foresee the outcome of Abu Nazir's long-awaited attack."
Homeland was recently officially renewed for a second season by Showtime.
Homeland airs on Sundays at 10/9c on Showtime in the US. The show will be broadcast in the UK on Channel 4 next year.