Husband from a straight married couple (no kids, though) make friends with a bi woman. Husband is working away from home for a time, and tells wife he would like "naughty" pictures. Wife gets BiF to help take pictures. BiF starts by just taking pictures of Wife, but talks Wife into allowing BiF joining her in the pictures. Wife and BiF go from taking pictures to forgetting camera and having serious lesbian sex! (Wife did not know she was bi) When Husband can finally get home, Wife and BiF have a 3some with him to celebrate. Couple find they enjoy this so much, they wind up a trio.