The family in "Once Upon a Time" adds numerous security measures to their home as they become more and more fearful of intrusion and theft. Gordimer is a South African writer, and in her story she indirectly alludes to the societal situation in the country during the policy of apartheid. The family is obviously white, and they feel threatened by the poor Black people who live outside their affluent suburb.

The first security measures the family takes include a subscription to the Neighborhood Watch, a sign on the gate that says, "You Have Been Warned," and insurance "against fire, flood damage and theft." They also only hire a housemaid and gardener who are "absolutely trustworthy" and "highly recommended by the neighbors."

The wife insists that the family needs additional security. To please her, the husband adds "electronically controlled gates" with an intercom system between the gate and the house. The maid is still frightened of thieves, and so the husband has bars put on all the windows and doors and also installs an alarm system. As unemployed indigents begin to loiter in the streets outside the house, the wife's mother pays to have the wall made higher.

As a final innovation, after comparing security devices on other homes in the area, the husband and wife decide to have coils of barbed wire—"shining metal serrated into jagged blades"—installed on top of the wall. This results in tragedy as their child, while playing, becomes trapped and mangled in the sharp coiled wire that had been set up to supposedly ensure their safety.