Generate a question about the following movie plot: Ray Milland plays Dr. Allan Fields, a nuclear physicist who works for the Atomic Energy Commission in Washington, D.C.. But Fields is also a spy working for an unnamed foreign power. Through an elaborate series of plans and devices, "tradecraft", Fields, as ordered by his "case officer",[3] takes sets of photos of top-secret documents, using a Minox camera, and passes these through a vast network of foreign-power "couriers"[4] to New York City, and thereafter overseas to an enemy country (implied by the final courier's plane's destination of "Cairo",[5] certainly a thinly-veiled reference to "the East", without actually naming the Soviet Union). The latest canister of microfilm which Fields sends out is intercepted by authorities after a courier is killed in a freak traffic accident in Manhattan, with the undeveloped microfilm canister in his hand. The FBI develops the microfilm, analyzes its contents and constructs a list of probable suspects within the AEC, one of whom is the "custodian"[6] of the subject document, and who is initially interrogated. The custodian having apparently been cleared of espionage charges, the custodian's subordinates, including Fields and his immediate AEC colleagues, have all come under suspicion by the FBI, and agents are assigned to "tail" each one, but it quickly becomes apparent that Fields is the "prime suspect". Fields' case officer becomes aware of this and sends him a "flash message", in a Western Union telegram, to destroy all his "spy-craft" apparatus and to leave immediately for a "safe house"[7] in New York City. Now scared and paranoid, Fields stays overnight in the safe house, a cheap hotel, waiting for a "signal" (as usual, throughout this film, three rings on the phone, a hang-up, followed immediately by three rings, followed by another hang-up)[8] from his case officer on the hotel's hall phone. After Fields has been so signaled by his case officer, his trail eventually leads to the Empire State Building. While at the 86th-floor observation deck, Fields meets his...
A:
Fields waits on instructions for how to escape what?