Sex and Lucia is the story of Lorenzo (Tristan Ulloa), a Madrid writer struggling with his second book, and his waitress girlfriend Lucia (the luminous Paz Vega). Fearlessly direct, Lucia approaches Lorenzo in a bar and announces that she's read his debut novel and decided beyond doubt that she's in love with him. Within hours they are in his bed, and from that time forward they live together, at first enjoying rapturous episodes of energetic sex (rendered far more explicitly than anything an American filmmaker would dare) and later settling into cozy domesticity. As in Eden, the serpent in their garden appears as a question mark. Lucia reads Lorenzo's new book and finds it proficient rather than dazzling. She thinks the second novel is too happy; she misses the tragedy of the first.
We don't know if Lorenzo even publishes this second work of fiction. But soon his agent Pepe (Javier Camara) appears to revisit an earlier proposal that Lorenzo write a fictional account of a mutually ecstatic and deliberately anonymous one-night stand Lorenzo had several years ago with a blond Valencia chef named Elena (Najwa Nimri). For added fodder, Pepe reveals that Elena has relocated to Madrid and that her single rendezvous with Lorenzo has produced a daughter, Luna (Silvia Llanos), now four. Lorenzo is intrigued, and Pepe arranges for him to meet Luna at her school without having to encounter Elena.
A more conventional filmmaker would assemble these narrative ingredients to test Lorenzo's natural paternal instincts against his yearnings to be a faithful lover to Lucia. Instead, Lorenzo plummets disastrously into an unseemly relationship with Luna's barely legal-age nanny Belen (Elena Anaya). Though subsequent scenes attest definitively to her sexual maturity, Belen is so youthful we at first think her another school child. In short, lust is not one of the seven deadly sins by accident. Belen lures Lorenzo with confessions about masturbating while fantasizing about him and even naughtier tales of watching pornographic videos starring her own mother. Lorenzo's involvement with Belen is indisputably sinful and indisputable evidence for why "lead us not into temptation" is a central plea in the Lord's Prayer.
In brilliantly paired ironic developments, Lorenzo draws artistic inspiration from his assignation with Belen while his extensively embellished account of a love triangle among Belen, her mother, and her mother's lover is greeted with unbridled praise from the reader who matters to him most: Lucia. On repeated occasions during this stretch of the movie we are not immediately certain whether we are watching "real" scenes or "enacted" scenes from Lorenzo's novel in progress.
At the end of Annie Hall, Woody Allen's Alvy Singer turns to the camera and apologizes for the happy ending of a play he's written, explaining how artists often try to make work out in their fictions what they can't make work out in their real lives. Medem is up to something comparable. The story he's written for Sex and Lucia is inevitably tragic for someone: either Elena who leaves her home in search of her baby's father, Lucia who stands to be abandoned, or Belen who needs to encounter adults capable of restraining themselves, or all three. But even as Medem sustains the narrative tension over the forks and intersections of these sad possibilities, he guilefully asserts the craft of revision. Announced through a bedtime story Lorenzo tells Luna, Medem warns that Sex and Lucia has a hole in its end through which one can escape to its middle and change the course of what follows. Just as the sex is both honest and prurient, a barker's come-on to a metafictional puzzle, Medem is an illusionist to the end. He shows us an empty hat all at once nesting a dove. In the end, we have heartache or healing, neither or both.