A married couple loses their children while on a family trip near some caves in Tijuana. The kids eventually reappear without explanation, but it becomes clear that they are not who they used to be, that something terrifying has changed them.

Lidia is a responsible and dedicated maid for a hugely wealthy, elderly Tijuana matron who loves only her pet whippet. Rafael is a quiet and dignified janitor who buys a new pair of shoes to celebrate his imminent retirement from the large corporate facility where he's worked for 30 years. When Lidia's boss dies, leaving everything to her dog, and Rafael's plans get derailed, they both turn to criminal subterfuge to get what their harsh lot in life has denied them.