Sam’s mother has won a berth on a two-week Mediterranean cruise but has given Sam her ticket because she can’t miss her best friend’s divorce party… and maybe because Sam has had a bit of a nervous breakdown.

But as non-binary Sam is an ex-climate activist, they are planning to use their time on the ship to stir up some trouble and make people aware of how cruise liners are ruining the planet.

In one of the bars, Sam is approached by a member of the crew, Amelia, a dancer from the ship’s entertainment programme. They are immediately attracted to each other and agree to meet regularly for cocktails. We learn that Sam and Amelia are polyamorous and both are in open relationships. Just before they jump into bed together, they discover that they share a partner, Tony, whom they both adore. The sex is put on hold as they come to grips with their situation and learn more about one another.

No jealousy is evident between shy Sam and audacious Amelia and they seem to be perfectly happy in their serendipitous “thrupple”. Individually, they call Tony and regularly share their personal experiences with him, which strengthens their bond.

Tony is a serious climate activist who has physically suffered and been imprisoned for the cause. Sam and Amelia want to make Tony proud and decide to join forces in a campaign to disable the ship in as many ways as possible.

Eventually they do end up in bed together but their relationship and plans are suddenly halted by Amelia being offered a part in a Broadway show. What will she do?

A good two-hander like this depends on strong characters and sharp dialogue, which Cruising has enough of, in order to qualify. There are numerous witty lines and a few laugh-out-loud moments.

And offstage, the Captain’s announcements become funnier and funnier, as he desperately tries to find out who is causing the mayhem on board his ship.

Cruising is hardly subversive but it gets its important message across without being too preachy.

(Eg I didn’t know that fleet operations in European waters emit the sulphur equivalent of hundreds of millions of passenger cars, severely impacting the air quality along coasts …but now, effortlessly, I know!)

I doubt, however, that its superficial exploration of polyamory is necessary to the plot and its view of open relationships is a tad rose-tinted, but it does add a little spice to the story. The play’s main aim is a call to action and a message that community, personal sacrifice and perseverance can bring positive results.