Convicted of armed robbery, Isa, arrives at the prison. Following her on her daily walk in the yard, it's clear that this is not the first time she has been there. As she embraces Dolores, a blond gipsy who has killed her husband, Rosa, a fragile and tender prostitute, and the other inmates, we feel that she is returning home. Yeserias women's prison houses a number of repeat offenders. Bonded by love and friendship, and dehumanised by the rules and regulations by which they are forced to live, its female inmates have lost the ability to function in a normal society. However when failed actress Mar arrives to start work at the prison, her ability to see these convicts as people gains her a new kind of trust. Desperate to inspire the prisoners, she starts a theatre group, Modulo 4. This group gives the women a new confidence, and through their performances they find the freedom to express their individual personalities and begin to learn to live as regular people once again.