My first observation is Haman's wife, Zeresh, and friends were the major contributors to his downfall. Haman still was the one who kicked it all off and kept it going but he was helped along his path of destruction by his own wife and friends.

My second observation is that as you read the book of Esther from front to back (not skipping around) I saw a shift of character focus.  The main character in the beginning is Esther with slight undertones of Mordecai.  Then in the middle of the story Mordecai is a greater figure, at least equal to all the other characters of the story.  Finally, there is no doubt Mordecai is the prominent character at the end of the story.

To elaborate on my first observation let us look at what happened in the story.  To summarize and paraphrase some (Esther 3:5 - 5:13) it all started when King Xerxes's high official, Haman, saw that a certain someone, Mordecai, would not give him any respect.  Haman not only thought of hurting Mordecai personally, but all his people too (doesn't that sound devilish?).  Haman gets King Xerxes to create a document proclaiming on such a date that the Jews are to be wiped out.  Mordecai hears about it and persuades Esther, who is Queen, to intervene on behalf of the Jews (Mordecai's people and Esther's people).  Esther prepares banquest number one, but for some reason does not have the opportunity to tell the King about her Jewish heritage then so she requests a second banquet.  Meanwhile, Haman goes back home and boasts to his wife and friends about being "the man".  His pride swells as he tells them about the private banquet that the queen invited him to with the King.  Then Haman makes the following statement which sets up his downfall.

" 'But all this gives me no satisfaction as long as I see that Jew Mordecai sitting at the king's gate.' 

His wife Zeresh and all his friends said to him, 'Have a gallows built, seventy-five feet high, and ask the king in the morning to have Mordecai hanged on it.  Then go with the king to the dinner and be happy.'  This suggestion delighted Haman, and he had the gallows built." (Esther 5:14)

That night King Xerxes didn't sleep, so he had the history of his reign read to him.  During the reading the instance where Mordecai uncovered an assassin's plot to kill the king was read to the king.  King Xerxes asked if any reward was given to Mordecai for this service and the answer was "nothing".  Morning comes and in walks Haman ready to ask the King to hang Mordecai, but before he can ask him his question, the King asked one of Haman - "What should be done for the man the king delights to honor?"  Of course, Haman thinking he was "the man of honor" says that you should give him one of your crowns, one of your robes, one of your horses and parade him through the city shouting "this is the man".  The king was pleased with that response and put Haman in charge of doing just that for.....Mordecai.  After being humiliated Haman "rushed home, with his head covered in grief, and told Zeresh his wife and all his friends everything that had happened to him. (Esther 6:1-13)

His advisers and his wife Zeresh said to him, 'Since Mordecai, before whom your downfall has started, is of Jewish origin, you cannot stand against him - you will surely come to ruin!'  While they were still talking with him, the king's eunuchs arrived and hurried Haman away to the banquet Esther had prepared."

While "ruin" does not necessarily mean death, Zeresh and company prohesy Haman's doom.  Even while they were still finishing their thoughts with Haman the entourage arrived to escort him to Esther's banquet number two. 

The banquet occurs and Esther reveals her Jewish heritage much to Haman's shock.  She asks the king for him to spare the destruction of the Jews and it is granted.  Moreso, the life of him who made the proclamation, Haman, is sentenced to death on the very gallows that his wife and friends told him to make for Mordecai, built beside Haman's house (Esther 7:8-10).  In addition, the same gallows saw Haman's sons hung on them later on (Esther 9:13-14).

So, the men of the family perished by the suggestion of Zeresh, Haman's wife, the gallows.  Then she prophesied things were going to get worse for them and it did.  I wonder and ponder what ever happened to Zeresh.

My second observation portrays Mordecai as a "networking" man, a man who was the perfect example of information and the proper use of it is power.

A Jewish Woman, Cousin, and/or Pawn On The Inside [Esther 2:7-18]
Mordecai is Esther's overseer or caretaker seeing that her parents have died.  He placed his plan in motion of having a high, governmental Jewish influence by having Esther submitted to the King's competition for queen.  His plan succeeded with flying colors, Esther became Queen and would be an awesome influence later for her people.

Right Place At The Right Time [Esther 2:21-23]
Mordecai revealed an assassins' plot to kill the king.  Mordecai heard about this plan, reported it to Esther, Esther reported it to the king-giving credit to Mordecai, the king investegated it, found it to be true, and recorded the whole instance in his records.

Mordecai Takes Issue With Haman [Esther 3:2]
Negatively, Mordecai gets noticed by Haman by not honoring him with a bow or possibly any other manner.  This places Mordecai on the wrong persons radar - Haman.

Mordecai Pulls His Strings for His People [Esther 4:12-14]
Esther, you're the Queen!  The king is not going to kill you!  Now stand and use the position I helped you get and the opportunity that is presenting itself before you or somebody else will be used. (Mordecai, paraphrased of course)

Mordecai Starts To Be Honored [Esther 6:11]
Haman gets the honor of "delighting in whom the king desires to honor".  What a way to start your career in being honored by having your enemy give you praise.

Mordecai Gains Power [Esther 8:9-10]
Mordecai jumps by leaps and bounds in power level when we see him here writing in the name of the king.

The Fear of Mordecai [Esther 9:3]
All the officials everywhere help the Jews because of a deep respect/fear of Mr. Mordecai.

Final Standing - Second To King Xerxes [Esther 10:3]
All to benefit the well being of his people, the Jews. Dedication.

Esther, it is a book that I have read many times but never saw these two observations until now.  A wife, Zeresh, that really aides in the downfall of her family and a character in the story which starts out with a low profile but by the end of the story you might as well name the story after him - The Book of Mordecai.
Zeresh disappears and Mordecai lives on as one of the greatest Jewish heroes of all time.