TORONTO - Blair Underwood was the son of a U.S. army colonel, spending his childhood living on military bases in the United States and Germany - perfect training for the actor's latest television role as a messed-up fighter pilot on the HBO psychotherapy drama "In Treatment."

Underwood's Alex, deftly portrayed by the actor with a simmering undercurrent of rage and paranoia, enters therapy like a bull in a china shop as he tries to figure out why he feels no remorse for dropping a bomb that killed 16 Iraqi schoolchildren. Irish actor Gabriel Byrne plays the soft-spoken and canny shrink who gently and methodically explores the cracks in Alex's armour to reveal a soul.

"My dad has always been real cool and laid-back, but there is a definite kind of mentality and sensibility with military personnel and the military lifestyle about duty to your country above everything else," Underwood said on a recent trip to Toronto to promote the show, premiering Monday night in Canada on the Movie Network/Movie Central.

"I intrinsically understand that whole culture and that whole environment, and that formed a great deal of who Alex is and how he presents himself."

The nine-week show is an ambitious one. Each of the 43 episodes, which air Monday to Friday in half-hour instalments, is a separate therapy session, with Alex just one of four regular patients. The fifth night shows Byrne as a patient himself in sessions with his own shrink, played by Dianne Wiest.

But it's the controlling and rigid Alex who's arguably the toughest nut to crack.

"He's one of my favourite characters of all the characters I've ever played because he's so complex and has so many different levels," said the 43-year-old Underwood, who's disarmingly handsome in person - and infinitely more laid-back than his character.

"He's kind of like the alpha dog, he thinks he's the best, and in this case he is the best in almost everything he does. But he's got so many issues underlying everything, and he ends up revealing so much of himself that you don't expect in the beginning because he's so resistant to opening up."

It's quite a departure from some of Underwood's more recent television roles: the altruistic billionaire on "Dirty Sexy Money" and the sexy schoolteacher on "The New Adventures of Old Christine" who has Julia Louis-Dreyfus's character all hot and bothered. He'll return to both shows once the writers strike gets resolved.

But he confesses he loves the experimental nature of "In Treatment" and how viewers are like flies on the wall watching intense and often painful therapy sessions.

"Each character is in therapy for a reason, but then over the nine weeks, layer after layer gets peeled back, and it's really compelling to watch these characters go through it," he says.

"Alex is the most reluctant of all the characters who come into therapy. But it really becomes a journey - the Alex you see at the end of the journey is almost unrecognizable from the first Alex we meet, and that's what I love so much about the show. It's brave and exciting to watch."

Underwood says he was also in awe of Byrne, an actor he'd always admired but had never met until the two signed on for "In Treatment."

"I really marvelled at his ability to deal with the sheer volume of work, the words and the dialogue, and then actually do the work and take the emotional journey that he has to take not only with the other characters, but with his own character," he said. "It was a lot - 43 episodes, and I only did nine. He did all 43. That's pretty amazing."