As stated, the two men commit premeditated murder here; they've carefully planned out their crime. Having invited David to the apartment, the two strangle the unsuspecting fellow with a rope (hence the title) and hide his body in a wooden chest in the living room. Then the creepy weirdos get ready for a dinner party which they're hosting; they have sadistically invited David's parents, his fiancee Janet Walker, and David's best friend Kenneth Lawrence who, incidentally, used to date Janice before David. Phillip thinks this is a bad idea and is a jittery mess over it, but Brandon, full of smug self-assurance, is vastly amused at the idea of having David's nearest and dearest unknowingly laughing and eating in the same room in which his body is hidden. He even has their maid move the table decor and food from the dining table to the chest in the living room, so that the guests will be serving themselves food and drink right over top of David's body. Thankfully, David's mother is ill and unable to attend, but David's father Henry Kentley is there, and has brought his sister Mrs. Atwater with him. Janet and Kenneth are awkward around each other and inclined to be angry with Brandon, suspecting that he has invited Janice, her old flame, and her new fiance to embarrass them all for his own amusement. They're partially right.
This is a brief summary of the plot of Rope; in my next post, I'll discuss the themes explored in the film and give my thoughts on the movie as a whole.