Mormonism is polytheistic but, ironically, the Book of Mormon is not. The following verses are typical of what the Book of Mormon says about the nature of God. Nothing here sounds like the "plurality of gods" which currently is taught by the Mormon Church.
And as I spake concerning the convincing of the Jews, that Jesus is the very Christ, it must needs be that the gentiles be convinced also that Jesus is the Christ, the Eternal God (II Nephi 26:12).
And now, behold, this is the doctrine of Christ and the only and true doctrine of the Father, and of the Son, and of the Holy Ghost, which is one God, without end, Amen (II Nephi 31:21).
And because he said unto them that Christ was the God, the Father of all things, and said that he should take upon him the image of man & and that God should come down among the children of men, and take upon him flesh and blood, and go forth upon the face of the earth (Mosiah 7:27).
And now Abinadi said unto them: I would that ye should understand that God himself shall come down among the children of men, and shall redeem his people.
And because he dwelleth in the flesh he shall be called the Son of God, and having subjected the flesh to the will of the Father, being the Father and the Son
The Father because he was conceived by the power of God; and the Son; because of the flesh; thus becoming the Father and Son
And they are one God, yea, the very Eternal Father of heaven and of earth (Mosiah 15:1-4).
Teach them that redemption cometh through Christ the Lord, who is the Eternal Father (Mosiah 16:15).
Now Zeezrom saith again unto him: Is the Son of God the very Eternal Father?
And Amulek said unto him: Yea, he is the very Eternal Father of heaven and of earth, and all things which in them are; he is the beginning and the end, the first and the last (Alma 11:38-39).
Behold, I am Jesus Christ. I am the Father and the Son (Ether 3:14).
Jesus is the Christ, the Eternal God (Title page, Book of Mormon).
And honor be to the Father, and to the Son, and to the Holy Ghost, which is one God. Amen (The Testimony of Three Witnesses, Book of Mormon).
From Doctrine and Covenants:
Which Father, Son and Holy Ghost are one God, infinite and eternal, without end.
Amen (Sec. 20, vs. 28).