Written by the remarkable Donald P. Bellisario, this series basically relates the life of Thomas Sullivan Magnum (Tom Selleck), a retired U.S. NAVY official that have been in the Vietnam war.
Now he lives in Hawaii working to solve mysteries and help people as a Private Investigator ("P.I.").
The series also shows TC (Roger E. Mosley) and Rick (Larry Manetti) - both are Magnum friends that met him in the Navy. Jonathan Quayle Higgins is a british house keeper that works for Robin Masters, a famous book writer that allowed Magnum to live in his mansion after a successful job he made for him. There're also Zeus and Apollo, two doberman dogs that together with Higgins will make a nice team to bother Magnum (and bring a lot of fun) in many episodes.