Tonight's the night we learn who gets hit in that explosive West Wing finale.

The Emmy-winning White House drama returns to CTV/NBC at 9 p.m. with an ambitious two-hour episode co-star Rob Lowe calls "the finest piece of writing I've ever read."

Brace yourself for casualties. Wounded characters are rushed into surgery as others flash back to Democratic candidate Josiah Bartlet's (Martin Sheen) march into the Oval Office.

There are over 100 speaking parts in the season-opener, with the entire recurring guest cast, including Stockard Channing, Tim Matheson and Tim Busfield making the scene.

Despite the accolades, some critics took Aaron Sorkin to task for the shoot-'em-up cliffhanger, which seemed a Muldavia-like ending to what had been to that point a noble, measured series of very human stories.

On a visit to the West Wing set on the Warner lot this summer, just before the season opener went into production, Sorkin himself defended the cliffhanger before a room full of TV critics.

"It was actually the one moment in the entire season that I planned ahead," said Sorkin, who usually writes on the fly, staying just ahead of that week's shooting deadline. Lowe, who also mingled with critics on the TV tour last summer, confirmed that Sorkin pitched him tonight's script "almost word-for-word" well over a year ago.

Neither would say who gets hit, but the action picks up "two minutes after" last season left off.

"I was really turned on by the drama (of an assassination attempt), all the events that occur in the minutes and hours after an event like that," Sorkin said.

The producer confirmed that Moira Kelly, who played political consultant Madeline Hampton, is off the show, although don't look for her to take a bullet tonight. "She is a fantastic actress and a wonderful woman and it didn't click on the show, much more my fault than hers," he said. "She'll be missed, but we both wanted to move on."

Anna Deavere Smith (The American President) is joining the cast as national security advisor and John Larroquette also guests as a flinty White House lawyer.

As well, look for the relationship between Josh (Bradley Whitford) and his assistant Donna (Janel Moloney) to heat up. "There remains great chemistry between Brad and Janel and we want to explore that at every opportunity," Sorkin said.