All About Love, set in 1820, follows Alasdair Cynster, better known as Lucifer, on his journey to escape the curse of love. Alasdair travels to his friend and mentor's house only to find his friend has just been murdered. Aided by a local, Phyllida Tallent, in his search to find the killer he also finds himself unwilling to run from the curse any longer.

Lucifer, after seeing the rest of the males in his family give into the family curse and marry themselves off, leaves London and the ton to avoid a similar fate. He heads to Colyton, a place where he is sure to avoid any similar temptation. His friend and mentor in the field of collecting, Horatio, has invited him to visit and appraise a very valuable find.

When Lucifer arrives in Colyton, he walks into Horatio's drawing room to find Horatio has been stabbed with a letter opener just moments before. As Lucifer is examining his friend and the scene surrounding him, he realizes that he is not alone. Before he can turn to protect himself, he is knocked out with a halberd, a thirteenth century weapon consisting of a battle ax and a pike on a pole about six feet long.

His attacker is Phyllida. Phyllida, having slipped into Horatio's house for alternative reasons, walks into the drawing room to find Horatio murdered. She turns him over onto his back. Then she hears a call and footsteps approaching. Thinking it is the killer returning to the scene of the crime, Phyllida backs into a corner to hide herself. As Lucifer is kneeling over the body, she realizes by his actions that this is not the murderer, but accidentally knocks the halberd off of the shelf. She tries to turn it away from him but is only partially successful. Lucifer is hit with the pole.

Phyllida touches his cheek, and after seeing that he is still alive, leaves the scene, not wanting to explain her presence in Horatio's house. Although he is found and taken to jail as the suspected murderer, Phyllida convinces her father, the magistrate, that this man is not the killer. She cares for him in her manor as he slips in and out of consciousness.

When Lucifer begins to recover, he realizes that Phyllida was in the house when she touches his cheek once again, thinking he is sleeping. Phyllida will not tell why because she promised her friend that she wouldn't.

As Lucifer and Phyllida spend their days searching for the murderer, Lucifer continues to question her about her presence. She continues to decline to tell because her friend continues to decline to give her permission. However, as multiple attempts to kill Phyllida occur, Lucifer is convinced that she must know something that the killer does not wish her to know.

As the pair continue to put the clues together, and question the locals, they continue to get closer and Lucifer spends his days seeking her hand in marriage. This is made easier when her father lets her stay at Horatio's house, which was willed to Lucifer, after one very close attempt on her life.