George (Tim Getman), Harris (Rob Jansen), Jerome (Tom Story) and Montmorency (Alex Mills) are the titular three men and dog. (Koko Lanham)

Last month, Alex Mills played Hamlet. Before that, he was Iago, Romeo and Jekyll/Hyde. What’s next for the two-time Helen Hayes- award winner?

“I’m a talking dog,” he says.

The dog in question is a droll fox terrier named Montmorency, who goes on a boating vacation in Synetic Theater’s new play, “Three Men in a Boat (To say nothing of the dog).”

In playwright Derek Goldman’s first adaptation of Jerome K. Jerome’s 1889 travelogue, the dog was played by a pillow.

“People fell in love with it,” Goldman says, recalling the production he directed in 1997, where the actors animated and spoke for a throw pillow. “Of course, Alex far surpasses the pillow.”

The Synetic show — Goldman’s second adaptation — follows three good friends and their dog on an ill-fated boating trip up the Thames. (Pieces of living-room furniture represent the boat.)

What was supposed to be a relaxing vacation turns into a mighty struggle as the men face fearsome foes, such as a tin of pineapple that refuses to open. The struggle results in grievous injuries for all three men, but Montmorency comes out unscathed.

The dog, probably the least bumbling member of the crew, is against the trip from the beginning.

“There’s nothing for me to do. Scenery is not in my line, and I don’t smoke. If I see a rat, you won’t stop; and if I go to sleep, you get fooling about with the boat, and slop me overboard. If you ask me, I call the whole thing bally foolishness,” Montmorency says.

Sort of: Mills delivers this speech as an expressive series of barks, which are expertly translated by his owner, Jerome.

Montmorency can speak English when he feels like it, using the same upper-crust accent as his owner.

“He takes on Jerome’s personality, which is very classy,” Goldman says. “The humor comes from the mixture of him being a dog — doing things like killing rats — and having this heightened dialect and sensibility.”

Mills’ muse was Jackie, a Jack Russell terrier that’s “like a child” to the play’s choreographer, Irina Tsikurishvili, Mills says.

“Jackie’s energy is just so high and boundless,” he says.

Doggie exuberance comes easily to Mills. Throughout the 90-minute play, he bounds around on all fours, makes messes for the sheer joy of it and parades proudly when he catches a water rat.

Tim Getman, who plays George, now knows the exhaustion of vacationing with a real-life terrier.

“When there are very physical scenes and we are all out of breath, Alex is like, ‘What? Let’s do more!’ ”

Synetic Theater, 1800 S. Bell St., Arlington; through June 8, $35; 866-811-4111. (Crystal City)