A hidden lock locked to an inner side of a doorplate comprises a top seat assembly; a top rod; the top seat assembly being assembled to the top rod; a linking rod installed to a lower side of the top rod; a lower rod; a lower head; a top seat assembly; a resisting unit. The connecting shaft having a groove, plurality of slots, a plurality of holes, an upper engaging tube and a lower engaging tube. A bent stop is extended from the resisting unit. When a top rod reduces inwards, the stop will resist against a neck of the top rod to prevent a lower head to contact the ground. A pin device is installed for retaining the lock in high temperature.