Cry Terror! 1958 by dongono

Jim Molner, who owns and operates his own small New York City electronics firm, is asked by war colleague Paul Hoplin, the two having been in the same munitions company during the war, to build miniature time bombs as prototypes for a possible lucrative military contract. Paul is really the head of a criminal gang who is using the bombs to extort $500,000 from 20th Century Airlines by planting them on board various flights, only informing its CEO Roger Adams of their locations in the process of payment. Paul is able to implicate Jim as the bomb maker, preventing him from going to the authorities. Paul also kidnaps Jim, his wife Joan and their infant daughter Patty to use them further in his plot, using a divide and conquer strategy to get them to cooperate, in Jim and Joan never sure what is happening with the other and more importantly Patty. Paul who has no hesitation to kill them if they don't follow his instructions. The FBI is leading the investigation and indeed is able to identify Jim as the bomb maker by one of the bombs Paul tells them about. The only other lead they have is the person who they believe planted one of the bombs, airline passenger witnesses providing information leading to a composite sketch. That sketch is indeed a true likeness of Paul's female associate, who Paul and the others only refer to as Kelly and who believes she won't be caught, with the authorities having an entire country to scour to locate her. As the FBI follows Paul's instructions and works to catch Paul, Kelly and any other of their associates, Jim and Joan, largely on their own, have to try and find a way out of their predicament ensuring the safety of each other and Patty.