with telling readers that one of the tenants was invited by mistake.

And, oh yes, one was a bookie, one was a burglar, one was a bomber, and one was a mistake. Barney Northrup had rented one of the apartments to the wrong person.

Readers are given a hint that the unintended tenant might be Sydelle Pulaski in chapters 18 and 19. By this point, readers are likely to be very curious about her anyway, based on her quirky habits; however, it isn't until chapter 26 that readers are told exactly how and why Sydelle is at the Sunset Towers and why she technically shouldn't be. Otis Amber admits that he was hired by Northup to investigate six specific people. He was supposed to investigate Ford, Theodorakis, Hoo, Windkloppel, Baumbach, and Pulaski. Amber admits that he later discovered that it was Sybil Pulaski he was supposed to investigate. That would have changed who got Northup's invitation.

Judge J. J. Ford, George Theodorakis, James Hoo, Gracie Windkloppel, Flora Baumbach, and Sybil Pulaski. I made a mistake on the last one; I wasn’t aware of the mix-up until I looked into Crow’s early life for the judge. It seems I confused a Sybil Pulaski with a Sydelle Pulaski.

The tenant to whom Barney Northrup rented an apartment in Sunset Towers by mistake was Sydelle Pulaski.

Barney Northrup had carefully chosen whom he wanted to live at Sunset Towers.  Each of the potential tenants whom he then aggressively courted had some connection to Sam Westing.  It is not revealed until later which of the tenants was the "mistake" (Chapter 1), but throughout the Westing Game, Sydelle stuck out because no one could figure out her connection to the game's inventor.  Sandy McSanders, the doorman and one of the Westing heirs, compiled a notebook listing everything that was known about each of the players.  On Sydelle Pulaski's entry, he answered the section about her "Westing connection" with only a question mark (Chapter 18).  Later, Judge Ford uncovered a transcript of an interview with a childhood friend of Bertha Erica Crow, credited to a Sybil Pulaski (Chapter 19).

The "mistake" was caused by Otis Amber, a private investigator hired by Barney Northrup to investigate the six people originally sought as tenants for Sunset Towers.  They were supposed to be J.J. Ford, George Theodorakis, James Hoo, Gracie Windkloppel, Flora Baumbach, and Sybil Pulaski.  Sybil Pulaski was a close friend of Crow, who turned out to be Westing's ex-wife.  Amber mistakenly misread her first name, Sybil, and ended up investigating a Sydelle Pulaski instead (Chapter 26).

Sydelle Pulaski, the bilingual shorthand-taking secretary, was an heir who should not have been included in the gathering of heirs at Sunset Towers.  Sam Westing (working, doubtless, as Barney Northrup or another of his aliases) was looking for a woman named Sybel Pulaski, who had been a dear friend of his wife in her girlhood, and had lived in the same apartment building.  But there was a confusion about the names, and Sydelle Pulaski, the spinster with an inferiority complex and a penchant for exhibitionism, was chosen instead.

Sydelle adds a great deal to the story, however, and becomes one of the most interesting characters (even if she is a bit annoying along the way.)  Through her friendship with Angela Wexler, Sydelle grows a great deal and manages to overcome many of her own problems during The Westing Game.  She is instrumental in the "solving" of the will (in which no one actually wins, but each comes out $5000 richer anyway) since she is the only one who took a copy of the will while it was read.  She did it in Polish, too, which meant that she would be the only one able to read it among the heirs.  This cleverness kept her at the center of the game for quite a while.

Sydelle's friendship with the much-younger Angela, and her ability to change and grow when faced with her own shortcomings (even at an age when most people's characters are considered set) is one of the most hopeful in the story.  She becomes less concerned about what others think of her, and less desperate to be "noticed".  This leads to a change in her whole attitude toward life, and she eventually becomes much more at ease socially, and ends up marrying her boss.  The Westing Game gave Sydelle Pulaski much more than money ever could.

The many pairs of tenants in "The Westing Game" all seem to have strong connections to Mr. Westing, especially considering they are all potential heirs to his multi-million dollar fortune. As they are going about their process of discovering his riddles and clues left behind, however, there is one character who seems to be a mistake—one who has little understandable connection to the late Mr. Westing.

Sydella Pulaski has a vague backstory and no connection to any of the other characters or Mr. Westing, making her mysterious and suspicious. She became a tenant apparently by mistake since she has no defined connection. In spite of her separation, though, she still takes kindly to Chris, and she participates willingly in the game.