Mechanism for retaining and releasing pump down plug

An apparatus for retaining and releasing a pump down plug, the apparatus comprising:

• an outer housing comprising a housing recess;
• a shifting sleeve that contains the pump down plug and is disposed within the outer housing and configured to slide within the outer housing, the pump down plug being elongated and having a nose end and an opposing end and the pump down plug defining a plug recess that extends below an outer diameter of the pump down plug at the plug recess between the nose end and the opposing end;
• and
• a retaining element configured to engage the plug recess of the pump down plug to retain the pump down plug, the retaining element being restrained from outward movement by the outer housing in a first position of the shifting sleeve;
• wherein sliding the shifting sleeve into a second position results in outward movement of the retaining element into the housing recess to release the pump down plug.