Ms. Plugg was a guard at Mr. Benedict's house in The Prisoner's Dilemma. She is described as have a rather square, "cinder-block" like head that looked as if it would slip from her shoulders at any moment. She is known to have been a women's wrestling champion during her time in school. She marveled over Kate's abilities and found the boys' knowledge quite incredible. She even clapped for Madge. Her opinion of Constance is unknown however, although it is assumed she likes the young girl as well. For the longest time should could not remember Sticky's name, and only by creating the mental note "fiddlesticks" (he fiddles with his glasses) could she remember it.
Ms. Plugg was at Mr. Benedict's house at the time of the Ten Men's attack. She was stationed in the front of the house and intercepted the children when they ran out that way. She refused to go into hiding and wanted to do her duty protecting the inhabitants of the house. As she ran off around the corner toward the Ten Man Kate had inconvenienced with her flashlight, the children sadly reflected that "Not even Ms. Plugg stood a chance against a Ten Man, even a disoriented one." This Ten Man was later revealed to be Hertz.
When Milligan finally returned from the Quarryside neighborhood, Ms. Plugg told both him and the children the disturbing news of how the "Whisperer" had been destroyed. She felt terrible about her failure and did not readily forgive herself, even when told it was not her fault. During the same evening, she was also the guard that Kate tricked into standing outside the basement door of Mr. Benedict's Other Property. This assignment was based upon mysterious orders from Milligan that no one but the children seemed to know about. She was described as looking relieved at being given a new task. After Kate, Reynie, and Sticky returned from the Monk Building she called the others over after berating Kate and the boys.
During the Battle of Third Island Prison, Ms. Plugg arrived in the car disguised as first a government contact and then a sentry. When Milligan failded to return or even to report in on the radio, she and Moocho Brazos left to go find him. Thinking that the roof would be a good point to survey the area from, she and the strongman headed up to the fourth floor. Unfortunetly for them, the Ten Man McCracken had the same idea. After a fierce but short fight, Ms. Plugg and Moocho were rendered unconscious. Milligan protected them from McCracken by shoving them into the elevator and jamming the door.
At the end of the story it is not revealed what happens to Ms. Plugg, although Ms. Argent refers to her as the security guard, so it can be assumed she retained her job. She presumably joined the party celebrating Constance's adoption.