Sandra meets Luis. Soon they move in together. He always acts cold and distant in the relationship, which leads Sandra to think that his nature can be caused by a lack of oxytocin, a hormone which acts on our nervous system managing social and sentimental behavior. Determined to change her relationship, Sandra gets to give him some dose of oxytocin. Luis changes his behavior completely, becoming a different person. He becomes more loving, more romantic, more sensitive. At first she’s delighted with his new identity, stills, as time goes by, she’ll discover two things: that the excess of love that he shows overwhelms her and that she’s got no right to modify the personality of the man she loves. She decides to stop giving him the dose and he is the same as always, even though she keeps the memory from those days lived with strangeness.