Hiroto and his wife Nodoka are married and love each other, but over the years their sex life has become stale and less frequent than before. They get invited to dinner by the Iseya couple, Masataka and his wife Saki, who they have met briefly before. The Iseyas openly show their affection to each other and as their actions get more and more daring, Hiroto's sexual desire is rekindled. After another dinner the Iseyas ask them, if they are interested in partner swapping. Hiroto hesistates but Nodoka tells him, she trusts him and the decision is his.