Magnum P.I. Season 4 ( Air Date 2021-10-01 ) Genre Action & Adventure, Drama, Crime category. Overview "Thomas Magnum, a decorated former Navy SEAL, returns home from Afghanistan and applies his military skills to become a private investigator in Hawaii taking jobs no one else will—with the help of fellow vets T.C. Calvin and Rick Wright, and former MI:6 agent, Juliet Higgins.".