In Madrid, Casada Campo, the beloved park of the townspeople, dawn Don Carlos and his servant Mosquito await. They cannot appear in the city during the day: two months ago, Don Carlos killed a noble caballero Alonso, son of Don Diego and brother of Lysarda, in whom Don Carlos was unrequitedly in love. This feeling did not stop him from simultaneously caring for another noble lady - Selia, which was the reason for the duel: Alonso was in love with Selya. Fearing punishment by the authorities and the revenge of Alonso's relatives, don Carlos was forced to hastily flee to Portugal, where Celia sent him a letter urging him to return and find refuge in her house, where it would not occur to anyone to look for don Carlos while he put in order the things that had been abandoned due to a hasty departure. But don Carlos has another reason to strive to Madrid: he dreams of wandering at night under the windows of Lizard, which he cannot forget, although now he can hardly count on her favor. Fate smiles at Don Carlos: while the caballero is waiting in the Casad-Campo of darkness, the nearby carriage of Aisarda unexpectedly overturns, and only the intervention of Don Carlos saves the woman's life. Covering his face with a cloak, he stubbornly refuses to give his name to the grateful Lizard, but in the end retreats before her perseverance. Lizard is shocked and indignant at the insolence of Don Carlos, but pulls herself together and, telling her savior that today her gratitude supplanted the thought of revenge, but that the next morning, Don Carlos can no longer be calm for his life, leaves him.
Meanwhile, Seli’s brother, Felix, unexpectedly returns to Madrid from a military campaign: he received a letter stating that appointing one of his fans Selya caused a duel between don Carlos and don Alonso, but she herself, fortunately, managed to slip away unrecognized . And Felix returns to protect the honor of his sister and intends to take the most severe measures for this, despite Seli's outrage and her strong protests. The argument between brother and sister is interrupted by the arrival of don Juan, who is engaged to Lizard and considers himself obligated to avenge the death of his future wife's brother. Don Juan tells Felix that he met a man very similar to the killer of Alonso, and tracked down where the suspicious stranger stopped. He asks his friend Felix to go with him and help identify this man, because don Juan does not have full confidence that this is don Carlos.
As soon as they leave, Don Carlos appears with the faithful Mosquito. Upon learning of Felix’s unexpected arrival, he wants to leave Seli's house right away, but the girl manages to persuade him to stay: she explains that their apartment is connected by a secret staircase to the lower floor, which is known only to her, and that, having learned about her brother’s arrival, she ordered walled up the bottom door, leaving only one exit - in her own dressing room. Don Carlos is touched by the girl’s courage and prudence, with which Celia took care of everything, but still does not dare to take advantage of such hospitality and is inclined to leave, but don Juan and Felix suddenly return. Carlos and Mosquito have no choice but to quickly hide behind a secret door. Seli's brother was scared to death because he got involved in a duel and mistakenly mistook a person for Don Carlos and killed him. It was not possible to hide unrecognized: Felix clearly heard how one of the soldiers who ran to the ring of swords called his name. Now he himself was in the position of Don Carlos: he needed to hide as soon as possible in order to avoid the punishment for the murder. But since, connected with the need to protect the honor of his sister, Felix can not completely leave Madrid, he decides to immediately change the apartment. At his order, the servants hastily take out all things, and very soon the house becomes empty: there is no one left in it, and the entrance doors are carefully locked - don Carlos and Mosquito suddenly remain trapped. They did not immediately realize this, initially deciding that everyone was asleep, but they soon became convinced that their assumption was incorrect. They barely have time to realize that they are locked without food in an empty house, where all the windows, including the attic, are locked with bars, as the owner of the house comes in - he was called by the police looking for Felix. After making sure that he is not here, and believing the owner’s words that Felix left Madrid a few months ago, the police leave the house where Don Diego, Lizard’s father, who likes the abandoned apartment very soon, enters. He immediately decides to rent it for Lizard and don Juan, and after a few hours new residents reign in the house. Lizard, like Sella, sets aside a room with a secret door, of which she certainly does not know anything, under her dressing room. Here, a servant of don Juan brings gifts from his master for the bride and her maidservant.
When everyone leaves and silence sets in, don Carlos and Mosquito get out of their hiding place and decide that Mosquito will change into a woman’s dress and go unnoticed out of the house, so that with the help of relatives and friends of don Carlos he will help to get out. The commotion caused by the loss of the dress, which Mosquito chose from a pile of gifts, raises all the asleep inhabitants of the house, even Don Diego. Suddenly appears wrapped in a cloak Selya - she begs Don Diego to help her hide from the man pursuing her. Don Diego, like a true caballero, rushes to the door, not demanding any explanation, to detain the fictional pursuers of Seli. At this time, from behind a secret door, a Mosquito dressed in a woman’s dress comes out, whom Don Diego, who returned in the twilight mistaking Selya, gallantly escorts him to the exit. During this time, Selya manages to explain everything to Don Carlos, who has left the cache, and to give him the key to the front door. However, she herself does not have time to leave: don Juan and Felix who came to him enter the room. Hiding behind the curtain, Selya hears that his brother, having discovered her disappearance and deciding that she went on a date with don Carlos, is determined to find and kill the offender; don Juan readily volunteers to help him.
In their absence, Lizard in the dark stumbles upon Selya and suffers from jealousy, tries to look into that person, but Selye manages to escape. And returning at this time, don Juan confronts don Carlos, but, not recognizing him because of the darkness, he accepts Lizard as a fan. While Lizard and don Juan shower each other with jealous reproaches of infidelity, don Carlos and Selya are hiding behind a secret door, where, unable to withstand all the experiences, Selya falls without feelings. Don Carlos faces a painful task: who to trust, whom to turn for help. He opts for the compassionate Beatrice, the servant of Lizard, but instead of her in one of the rooms he suddenly sees Lizard. The girl is indignant, but, fearing to be compromised, she is forced to hide Don Carlos in Beatrice's room.
Meanwhile, on the street at the door of the house, don Juan saw Mosquito and, seizing him, tries to find out where his master is hiding. And since he refuses to answer, mainly out of fear that don Carlos is behind a secret door and can hear him, Mosquito is locked in a room - until he decides to become more talkative, Left alone, Mosquito wants to hide behind a secret door and finds there grief that is grief-stricken : the girl heard don Carlos’s love confessions addressed to Lizard, and is determined to reveal to her rival the true reason for don Carlos’s appearance in this house, but here you can hear the steps and voices of don Juan and Felix, and Mosquito hastily hides in the cache, and Celia does not have time to do this . Don Juan tells Felix that the servant of don Carlos has been caught, and Felix asks to leave them alone: he hopes to find out from the servant the location of don Carlos, and at the same time his sister, But instead of Mosquito, friends find a woman wrapped in a cloak in the room. Taking her aside, don Juan tries to find out who she is, and before his insistence, Selya is forced to retreat - the girl throws back the edge of her cloak covering her face. Seeing the friend’s excitement from the other end of the room, the intrigued Felix also wants to find out the name of the mysterious stranger, and don Juan finds himself in a ticklish position: both - both brother and sister - trusted him, and he cannot betray either of them. Fortunately, at that moment, Don Diego's voice is heard outside the door, who became aware of the disappearance of Don Carlos's servant from the locked room and who demands that he be let in. Fearing to give Lysard a new reason for jealousy, don Juan hides Selya in his room.
Filled with a desire to find a servant, Don Diego orders to search the whole house, he himself decisively goes to the room of don Juan, but here on her doorstep appears Selia wrapped in a cloak. Don Diego and Lysarda have no limits to indignation: both accuse don Juan of treason - and here the servants bring Don Carlos, who categorically refuses to call himself the house owner in response to the demand of the house, asking for permission to leave this house unrecognized, but only with Sela. Don Diego promises the strange guest safety - and Don Carlos throws the cloak off his face. He explains to the stunned don Diego that he killed Alonso in an honest duel, and came to this house for Selia, with whom he was engaged - the play ends with universal reconciliation.
