‘Run’ takes a twisty route on its way to some funny moments

They’re acting strangely on a train.

In fact, Ruby and Billy are some of the most disruptive and annoying passengers in cross-country rail history. They get into loud spats. They belly up to the bar car and proceed to get hammered. They’re forever running from car to car. They cause extensive damage to their roomette. Geez, they even jump from the moving train.

I don’t think Amtrak will want them back.

Merritt Wever is Ruby and Domhnall Gleeson is Billy in HBO’s gimmicky but darkly funny and involving new limited series “Run,” created by Vicky Jones and executive produced by Phoebe Waller-Bridge (“Fleabag”), who also has a hilarious cameo as a taxidermist who delights in finding roadkill (don’t ask). When Ruby and Billy were college sweethearts, they made a pact: If one of them ever texted the one-word message “RUN” and the other responded in kind, they’d drop whatever they were doing and meet at a designated spot in New York City.

About 15 years later, Ruby is a harried wife and mother parked outside a big-box store in California, while the Irish-born Billy has become a world-famous inspirational author and speaker. Billy sends Ruby the “RUN” text, and on a mad whim, Ruby texts back and heads to the airport. Sure enough, Billy makes it to New York City as well, and without revealing anything about the state of each other’s lives, they agree to board an Amtrak train bound for Chicago and see where this whole journey takes them, in more ways than one.

The more we get to know Ruby and Billy, the LESS we like them — but to the credit of Wever and Gleeson, we’re keen to see what happens to these two irresponsible narcissists. As you might expect, even as they dance around whether or not they’ll sleep together and begin to share details of their respective lives, neither is being completely honest and there’s a whole mess of trouble closing in from multiple sides. Archie Panjabi shows up as Billy’s longtime assistant, who’s harboring some deep secrets and a stalker-esque obsession with Billy, while Rich Sommer does what he can with a thankless, hapless spouse-on-the-phone role as Ruby’s husband Laurence, who is slow to catch on to what’s really happening.

It takes a while for “Run” to find its footing — is this a drama with comedy, or a comedic farce with drama? — but when events heat up, we get some fantastically funny set pieces, including the brutal demise of one particular player. This is a well-filmed show. The sequences on the train are particularly impressive, as the camera seamlessly stays with Ruby and Billy as they race about, get caught in tight quarters and make that aforementioned leap from the train. Ruby and Billy are smart and calculating, except for the times when they’re careless and reckless. Their rash actions often land them in the boiling water, and it’s a coin flip as to whether we’re rooting for them or the boiling water.