"I was interested in how, whatever that dark past is - and I'm glad we don't really talk about it - how it has affected him. And I think it has contributed to his obsessive compulsive behaviour. He says that he promised his wife he would never go back to being whatever dark person that he was, but he makes an exception for this bad guy."
"This bad guy" is an intense Russian mob fixer played by Kiwi Marton Csokas, who despite carving himself out a very nice career in Hollywood, is perhaps better known around these parts as Dr Leonard Dodds from Shortland Street.
When we first meet Washington's character in The Equalizer, he's working in a giant hardware store. In what is fast becoming known as the film's signature scene, McCall utilises items from the store to creatively take down a phalanx of bad guys. "The stunt guy was a Navy SEAL and we had these martial arts guys, and they walked around that store coming up with crazy ideas as to what to do.
"I saw it with an audience for the first time in Toronto and they were getting into it. It was fun hearing the reactions. They were cheering when I put the hammer back.
"It is a popcorn movie, and it's steeped in a reality, but it's sort of a hyper-reality."
Although The Equalizer is very much a solo venture, Washington is keen to return to the team-up style of his previous film 2 Guns, in which he sparred with Mark Wahlberg.
"I'd like to do more of that. I have a nice two-hander with Will Smith, but I don't know if he's ever gonna do it. He developed a nice two-hander for he and I. I like them.
"Again, it's always scheduling and he's doing what he's doing and now I'm booked up for the next year."
With McCall proving himself a highly lethal weapon all throughout the film, The Equalizer represents something of a more physical role for Washington. Is that something he relishes?
"I don't shy away from it. I'm not looking to do that next. In fact I'm gonna do a Western next. I guess there'll be some cowboy punches. I'm really excited about doing a Western. I start riding horses in October to train for it. I have a great job. I get to drive trains, I get to fly airplanes. I get to ride horses. I kick some butt."