Nick has such an intriguing way of explaining the tense situation, doesn't he? First, let's put the quote into context. Tom, Daisy, Jordan, and Nick are discussing pleasantries over dinner. In the middle of dinner, Tom's mistress (Myrtle) calls. The first time Myrtle calls, Tom leaves the room and rushes into the house (perhaps to answer the phone). Daisy reacts strangely, and then follows Tom. However, the second time the phone rings, Daisy immediately shakes her head at Tom as "all subjects vanished into air" because of the tense situation (Fitzgerald 16). Nick has absolutely no idea how to handle this and remembers trying to look at everyone without actually staring into their eyes. Then Nick makes his statement:
I couldn't guess what Daisy and Tom were thinking, but I doubt if even Miss Baker, who seemed to have mastered a certain hardy scepticism, was able utterly to put this fifth guest's shrill metallic urgency out of mind. (16)
A reader can take this statement, revealing the pins-and-needles type of situation, in one of two ways. The "fifth guest" can be the telephone itself, . . . a guest that keeps interrupting their vacuous conversation with its intense ring. More importantly, though, this "fifth guest" can be Myrtle herself, who must feel something is so urgent that she continues to call her lover even when he is at dinner with his wife and his cousin-in-law. Either way, Nick makes it clear that the "metallic urgency" revealed cannot be ignored.