In the noir-styled clip, Ariana and Mac play neighbors in an apartment complex who are totally, totally crushing on each other. They're crushing so hard that they go back to their respective studios and immediately start fantasizing about making out with each other through the thin wall separating their pads.
It's raining outside, and by the sheer force of their thirst, it starts raining inside, too. Mac gets so wet in the split-screen vid that he finally gets up the courage to go knock on Ari's door.
Naturally, she's been expecting him.