 Upon return to Earth, the Howards learn that a rejuvenation treatment has been developed to approximate the secret of longevity supposedly held by themselves; thus permitting Lazarus, who is grown old, to regain his youth.Note that Heinlein's basic concept in Methuselah's Children bears some similarities to George Bernard Shaw's Back to Methuselah, which Heinlein has mentioned having read.At the beginning of this book, Lazarus has grown weary of life and decides to die.