Bruce announces he's going on a cruise vacation while Robin visits his relatives upstate ... which is weird, because if he has nearby relatives, why the hell is Robin living with some wealthy stranger?
Coincidentally, Clark Kent is also taking a vacation, and bafflingly elects to take the same cruise ship as Bruce, despite possessing the ability to fly absolutely anywhere in the world instantly and for free. And guess what: The ship's so crowded, he's forced to share a cabin with Bruce.
"Look, it's either Wayne or the cast of Family Circus. Your choice."
All this feels less like an epic superhero team-up and more like the premise of a Jack Lemmon-Walter Matthau comedy. Clark has X-ray vision, and Bruce is the world's greatest detective, so how do they unravel the mystery of each other's secret identities? By getting changed in the same room together, of course. You're welcome, slash fiction authors.
"And as they leave, they run into the Joker and Luthor ..."
"... and they all get changed in the same room together."
"Ed, you have a problem."
However, their brilliant dual charade is thwarted by a window, and when light shines through the porthole, the two superheroes are revealed to each other.
Their pelvises are obscured to hide the plot twist that they accidentally put on each other's shorts.
Batman and Superman sagely agree to talk about the bizarre coincidence later. Also awkward: Once they've dealt with the present danger, Batman does acrobatics at the ship's dance for the enjoyment of the passengers, like an especially nimble cruise director.
Meanwhile, Gotham City has burned to the ground 37 consecutive times.