The film is divided into ten chapters. A secret vigilante society's nine members pass judgment on others. They meet to decide the fate of a wealthy businessman they have been keeping under surveillance known as “The Man Who Has Lived Too Long” and vote to dispatch him with a homemade bomb concealed in a cigar case. Members Forrest and Farallone are both in love with the sole woman in the group, Lilith. Forrest openly declares his love, but is spurned by Lilith, who is completely devoted to the "Cause". At a meeting later that day, as per their custom, Lilith deals playing cards, one at a time, to each of the society members; whoever receives the ace of hearts is to carry out the assassination. When Forrest is dealt the ace, Lilith offers to marry him that very day if it will give him courage. Forrest readily accepts, much to Farallone's distress. After the couple marries, the grief-stricken Farallone spends the night in the rain outside their apartment. The next morning, Lilith has been transformed by her love. She begs Forrest not to go through with the assassination. He replies that he is honor-bound to carry out his mission. He goes to the café where his target habitually dines and where Forrest works as a waiter. A distraught Lilith pleads with Farallone to stop Forrest. Farallone agrees to help the couple escape the society's punishment if Forrest fails his task, but extracts a promise of marriage from Lilith if Forrest is killed. Meanwhile, Forrest decides to abort his mission after he spies a young eloping couple seated next to the rich man’s table. When he returns to the secret council, the group's leader, Morgridge, sends the couple away to await Forrest's execution. Farallone begs the others to reconsider, but they are unmoved. When the cards are dealt, it is Farallone who gets the ace of hearts. Laughing, he carries out his part of the bargain with Lilith by setting offthe bomb, killing all present.
The film was originally shot with a different ending in which Forrest, Lilith and their baby are shown living in the mountains, believing they have escaped death with Farallone's help. One day, Forrest discovers the Ace of Hearts wedged in the bark of a tree and rushes back to the cabin only to discover Morgridge arriving, one of his arms amputated and his legs hobbled. Morgridge, who has survived the bomb blast, tells the couple of Farallone’s sacrifice and of his own conversion to the ideal of love as a greater force for changing the world than death and destruction. When Sam Goldwyn saw a screening, he declared the ending preposterous and ordered that it be reshot. The Ace of Hearts was the second of the five productions that Lon Chaney made for Goldwyn Pictures between his contracts at Universal Pictures and Metro–Goldwyn–Mayer. It reunited him with director Wallace Worsley and co-star John Bowers after their work on The Penalty, also based on a Gouverneur Morris novel. The film was one of Leatrice Joy’s last productions for Goldwyn before her move to Paramount Pictures the following year.
