"Midnight Swim with the Black Cat!" Well, that should be fun...(It was not fun.)

Also, I don't think the Cat even gets in the water this issue! From 1989, Marc Spector: Moon Knight #5, "Rockin' at Midnight" Written by Chuck Dixon, pencils by Sal Velluto, inks by Mark Farmer. 

Black Cat is not really integral this issue, though: Moon Knight had been trying to lure out his old foe, Midnight, and Cat gets involved in the jewel heist portion of events, intent on saving them for a fee from their insurers. (That was a very brief status quo for her, trying to establish her as a "good guy" on the side of law and order; I don't think it lasted long.) She rides along on the Mooncopter as Moon Knight and Frenchie chase Midnight's car, which ends up launched off of a bridge when it hits construction, with both Moon Knight and Midnight going into the drink. Still, Midnight isn't found.

Returning to his estate, Marc is greeted by Marlene, who wanted to make up with him, until she finds a platinum blonde hair on his uniform and storms off. Marc is a little perturbed that somehow that hair had stuck to him through a fight, a chase, and a swim: "That Black Cat was bad luck for me." He doesn't get out the door in time to chase Marlene and explain, but then Midnight was in his house! After a brief fight, Marc knocks him out, but apparently hadn't until then noticed he both looked and acted far younger than his old foe, Anton Mogart: this was his son, Jeffrey Wilde. And everything he had done to Moon Knight, had been basically his audition tape, to be his partner. I'm sure that'll work out great for him...Jason Todd would have died just the year prior; this era viewed sidekicks about as favorably as an inflamed appendix and they usually fared about as well. The last four pages of this one set up the Brother Voodoo storyline that would run to MS:MK #9

Ah, what could be more fun than night swimming? Um, just about anything, it's dark and cold. Not to say I haven't, though. And it's part of this great bit from the Looney Tunes Show: