"Professional Assassination is the highest form, of public service"- Chiun, reigning Master of Sinanju. The Destroyer series.
A product of an unlikely marriage of the Chicago Polish mafia and Japan's Yakuza, Mary Beth "Tambi" Baker is a ruthless and efficient crime family soldier, factotum, cut out, "force multiplier" and later American government sponsored mercenary unit leader. She never lets a prior friendship come between her and a clean and effective kill and is just as dangerous to her wielder (should said individual violate her meticulous and deeply held convictions) as her targets.
She has an identical twin sister, Sarah Beth "Bambi" Baker with a slightly rounder face and no scars (these from self inflicted cutting wounds) on her forearms. In most other ways, physically, the two are identical twins.
The only real means of distinguishing between the two twin sisters on first meeting are by the lily tattoo on Tambi's ankle (the personal mark of American Yakuza Warlord and Madam, Darcy Parker), (sister Bambi wears hers on her arm) and a roughly executed full back tattoo of a striking Tiger (rarely seen) on her (Mary Beth's) back. If her sister has/had a similar back tattoo, it has yet to be revealed in the series?
When the reader is initially introduced to Tambi, she appears to be little more than a hired chaperone for the "Parker Girls", escorts, call girls and prostitutes pimped by Darcy Parker in exchange for blackmail material, favors and money from the power elite and "jet set" of American society. But as the story proceeds, she becomes more of a central player. Tambi, in the initial print run of SIP, can be considered to be Yakuza Princess Darcy Parker's putative head of security and "hatchet woman" or "gun moll" who as the story unfolds fulfills a similar but somewhat different role to the one played by Virginia "Pepper" Potts to "Iron Man" Anthony "Tony" Stark in the Marvel MCU.
Eventually, in service to the memory of her dead father "Sonny" Baker and in order to free her baby half sister Katina Marie "Katchoo" Choovanski from the deadly attentions of the homicidal and controlling Darcy, Mary Beth takes it upon herself to coldly and efficiently remove Darcy Parker as head of the American Yakuza family (and servant to the shadowy "Big Six?), shooting her through the head with a silenced small caliber pistol (she arranges the scene to make the crime appear to be self inflicted) when Parker, obsessed and psychotically deranged with lust for her former girlfriend and sexual property Katina Marie; causes a major international incident by erratic behavior and out right incompetence, leading to the fiance of a favored candidate for the office of President of the United States to be revealed as a "D.U.C." (or Deep Underground Capability agent) put in place by Parker to control the potential President sexually and advance the goals of the Parker Apparat, thereby exposing her fellow Mafia overlords "The Big Six" as the real "Illuminati" and manipulators of the world in the SIP storyverse.
After Mary Beth assumes full control of the Parker girl operation subsequent to the deaths of her former employer and her sister "Bambi" (in an unrelated but crucial incident), she proceeds to hire and re-purpose supporting characters Beth and trained Sniper and (Elvis aficionado) Cherry Hammer to "clean up" the "mess" left after Darcy's cousin Veronica is targeted for "removal" as head of the now moribund organization.
Tambi initially also appears to have no love for Katina and even explains coldly and directly that she will kill her little sister without apparent remorse or affect, before dropping her off a 43rd floor balcony (a variation on an infamous means of softening up insurgent leaders for interrogation often employed by American CIA personnel and their mercenaries during the Vietnam conflict). Fortunately, the ruse is just that and Katchoo lands a few feet below the balcony at her former lover and employer Darcy's feet with Darcy listening to Katina's terrified confession, all the while.
Much later in the series, it transpires that Tambi hired Casey Femur as a trained accountant, who became bored with her role and eventually upgraded her to a field agent in place to look out for potential threats to little sister Katchoo. Much later, after Casey's divorce from SIP supporting cast member and lawyer Freddie Femur, Tambi and Casey become romantically involved.
During Francine's kidnapping storyline, Tambi again has her little sister protected without her knowledge by having one of her agents in place to keep her safe from the equally brutal and driven multiple murderess Veronica.