Claude Leffingwell (Hamilton Revelle) and Anne Smith (Elsie Esmond) marry against the advice of the eugenicist Dr. Horace L. Dickey (Dr. Harry J. Haiselden), who warns that Claude is genetically unfit. Sure enough, their child (Henry Bergman) is born severely deformed and will require major surgery to save his life. Dickey recommends against the surgery, saying that it would only prolong the child's misery. That night, Anne dreams about the surgery to save her child and the tragic life he will lead.
The Black Stork contains examples of:
- Appeal to Nature: Dickey argues that God made Leffingwell Jr. defective, and God intended for him to die.
- Broken Aesop: In some ways, the film unintentionally promotes the social model of disability. Despite the title cards' insistence that Leffingwell Jr.'s genes make him defective both physically and mentally, there's no evidence that he was born insane, and his deformities only rarely cause him any inconvenience that doesn't involve other people. In fact, it seems like he would have turned out fine if not for everyone treating him like a freak.
- Bury Your Disabled: The film's main Aesop is that it's better to let disabled infants die than save them, since they will only live unhappy lives. Harry J. Haiselden (who plays the film's physician, who's based on himself) did exactly that, leaving a baby boy with birth defects to die after persuading the boy's parents it was the best thing. After he had been acquitted by a jury, Haiselden launched a massive public campaign in defense of his action, the film being one part, and it got disturbingly high support.
- Cradle of Loneliness: After Leffingwell Jr. leaves home, his mother sleeps holding a pair of his old crutches.
- Fate Worse than Death: Footage of the defectives who inhabit mental institutions is shown, with normal characters lamenting their existence and wishing they could be freed from the "sentence" of their lives.
- Framing Device: Genetics expert Robert Worth explains to his daughter Alice's suitor Jack Gayson why he must submit to a thorough physical examination before he will be allowed to marry Alice, first by giving him a tour of some institutions, then by telling him the sad story of his old friend Claude.
- Happily Ever After: Jack passes his medical examination and rushes to Alice to tell her the good news. Alice says, "And we'll be happy ever after."
- In the Blood: Claude himself is perfectly normal, except for a "blood taint" from his grandfather's affair with an impure servant. As a result, his child is born hopelessly defective.
- Iris Out: Iris in and out are both used often as scene transitions.
- Mercy Kill: The film advocates putting defectives out of their misery as soon as legally possible.
- Never Given a Name: Seems likely for Leffingwell Jr., who is never referred to as anything other than "the Leffingwell child" or just "he."
- Ripped from the Headlines: In 1915, Harry Haiselden was involved in a major controversy because he convinced the parents of a syphilitic infant, John Bollinger, to let him die instead of sending him into surgery. The Chicago Medical Society later expelled him over his continued pro-eugenics speeches and promotion of The Black Stork.
- Title In: "One Year Later," when the Leffingwells' friends Tom and Miriam Watson celebrate the birth of their normal, healthy child.