Like “Y Tu Mamá También,” “Sólo Con Tu Pareja” — literally, “Only With Your Partner” — is a rambunctious sex comedy shadowed by mortality. Tomás is hardly a smooth-talking lady-killer; rather, he uses a combination of boyish sweetness and neurotic, puppylike eagerness as his main tools of seduction. He is a little too successful, enticing a nurse (Dobrina Liubomirova) into his bed while his randy boss, Gloria (Isabel Benet), is waiting for him across the hall. Tomás has lured her into the apartment he has borrowed from a friend, Mateo (Luis de Icaza).
As Tomás races back and forth along the window ledge, the movie has the breezy insouciance of a classic bedroom farce. But the lighthearted mood is disrupted by the possibility of true love — incarnated in a new neighbor (Claudia Ramírez), who lives between Tomás and Mateo and who has a fiancé — and also by the specter of death.
The nurse, feeling spurned and neglected, plays a cruel prank on Tomás, altering blood test results to suggest that he is H.I.V.-positive. This leads to some anguished soul-searching and also, rather improbably, to a madcap chase that ends on the observation deck of the Latin American Tower, Mexico City’s answer to the Empire State Building.
Mr. Cuarón never quite finds the tone that would allow him to fuse belly laughs with the horror of illness and death, but then perhaps Pedro Almodóvar is the only filmmaker able to mix darkness and light in that way. Still it is hard not to admire the younger man’s cheeky self-confidence, and hard not to enjoy the dexterity of his camera movements and the flair with which he attempts both low comedy and high melodrama.
The promise he showed in “Sólo Con Tu Pareja” has already been realized and exceeded, but there is something gratifying about witnessing such talent in its fledgling state.