U.S. Marshal Mary Shannon has a relatively simple day ahead of her: Pick up federally-protected witness, Tasha Turischeva, and get her situated in her new living situation with the help of her partner, Marshall Mann (yes, his name is really "Marshall"); make sure her sorta-kinda boyfriend, Raphael, picks up her ne'er-do-well younger sister, Brandi, from the train station, and survive the "surprise" birthday party her man-crazy mother, Jinx, has planned.
However, when Mary learns that the teenage son of another one of the witnesses under her care, a former hit-man Frankie Santoro, a.k.a. Frankie "Nuts,'" was murdered, all of her best-laid plans are shoved onto the back burner. And for that she's almost grateful, especially if it means that she might have to miss her own party...
Mary now finds herself faced with two questions: Was Frankie Junior killed by someone from Frankie Senior's past, which would mean that Frankie's old colleagues have figured out where he is? And how do you tell a mafia hit man that his only son was murdered? In order to keep Frankie from flying off in a blind vengeful rage (and blowing his cover), Mary has twenty-four hours to find and apprehend Junior's killer and still get to her birthday party on time.
Meanwhile, she's still left with her other tasks for the day, personal as well as professional-all of which would be a heck of a lot easier if Mary could explain to her loved ones what she actually does for a living. But for the safety of her witnesses, her family and herself, no one can know that she's a Federal Marshal attached to WITSEC. They think she's a glorified courier...which is why Raphael gets bent out of shape when Mary's sister Brandi steals his car and Mary won't come handle the situation, and her mother Jinx becomes distraught because her daughters aren't getting along. Mary can't tell them that she has to spend the day investigating a homicide-while cleverly avoiding confirming the local law enforcement's suspicion that the victim was in WITSEC-and solve the crime before all hell breaks loose.
After running herself ragged all day chasing leads and coming up empty-handed, it's ultimately Brandi's innocent birthday gift-and peace offering-that helps Mary crack the case. But before Mary can collapse in heap, she remembers that she has one final task before she can turn in for the night. At three in the morning she returns to the apartment of her new witness, Tasha, with the bag of groceries that were promised hours earlier and as her own peace offering, some magazines to help Tasha pick out the new pair of breasts she was promised as part of her deal with the federal prosecutor.
Happy Birthday, Mary.