Teresa, a cleaning lady from the Huesca police office, gives his son a USB drive she bought online.
Her son, Alejandro, gets upset when he finds out his mother's gift it's not new, and it contains a hidden folder that the previous owner didn't delete. The folder is protected with a password.
The mother, after her son's complaints, decides to return it. She looks for the receipt and travels to Zaragoza to give it to the seller, since she wants to complain that she paid the price of something new, for something used.
That same afternoon, the police find the dead body of the seller inside his store. Teresa, and her son suspect that he was murdered because of the hidden folder from the flash drive.
