While both the 1950s and 1960s versions of "Dragnet" both had episodes entitled "The Big Mother", the shows are very different--with completely different plots.
This show begins with a startling discovery--someone has stolen a newborn out of the local hospital! Sure, the parents had twins, but I doubt if that is much consolation! Who did it and why? It is unlikely a kidnapping for ransom, as the parents aren't rich and no demand for money follows. So who did it and why? Tune in and see for yourself.
This is a particularly sad episode. It's well done and I am not complaining about how sad it is--just be forewarned! Fortunately, it does end well...or at least as well as you could expect.
By the way, I have no idea why these particular detectives investigate the case as they are assigned to the homicide squad--yet no murder has occurred. If anyone can explain this, let me know.