To those who deny the spirit of God, in the Book of Genesis, in the very first page, the same page that should be in all who claim and hold the Old Testament, There is this passage in Genesis 1:

"The earth was without form, and void; and darkness was on the face of the deep. And the Spirit of God was hovering over the face of the waters"

To those who deny the Son, there is many passages that would hint or even fore-tell of the Son of Man.

Proverbs 30:2-4

"Surely I am more stupid than any man,
And do not have the understanding of a man.
I neither learned wisdom Nor have knowledge of the Holy One.

Who has ascended into heaven, or descended?
Who has gathered the wind in His fists?
Who has bound the waters in a garment?
Who has established all the ends of the earth?
What is His name, and what is His Son's name, if you know?"

Another interesting thing of Note is from Genesis again, Genesis 19:23-24

"The sun had risen upon the earth when Lot entered Zoar.
Then the Lord rained brimstone and fire on Sodom and Gomorrah, from the Lord out of the heavens."

Read Carefully, did you catch that? Then the LORD rained brimstone and Fire on the City, From the LORD of the Heavens.

Two Lords? One calling on the brimstone and Fire from the Lord in the Heavens? And one who was Dwelling currently in the Heavens, who was the one not in the Heavens I wonder?

Another interesting thing of note once more is found yet again in the Book of Genesis:

"Genesis 1-26-27:
"Then God said, "Let Us make man in Our image, according to Our likeness; let them have dominion over the flesh of the sea, over the birds of the air, and over the cattle, over all the earth and over every creeping thing that creeps on the earth." So God created man in His own image; in the image of God He created him; male and female He created them."

"Let us Make man in Our image, according to Our likeness;"
"So God created man in His own image;"

Who was this "Our" God spoke of when He created man?

And again Genesis 2-3
"And on the seventh day God ended His work which He had done, and He rested on the seventh day from all His work which He had done. Then God blessed the seventh day and sanctified it, because in it, He rested from all His work, which God had created and made."

Why would God an all powerful being made of nothing but boundless infinity need to rest? Unless He's not just boundless infinity, but has a Body aswell. Almost as if there is the Son.

And again

Genesis 3-8

"And they heard the sound of the Lord God walking in the garden in the cool of the day, and Adam and his wife hid themselves from the presence of the Lord God among the trees of the garden."

Lord God? And He's walking in the garden?

God is a Physical Living Being. God is also Spiritual. God is also of other origin. He has a Spirit, He has a Body, and He has a Soul. Or (Mind, Body, Spirit) if you prefer that.

All of this to say, the Trinity is Biblical, the Trinity is Truth, and it's found in Genesis in the very beginning. There is not 3 God(s), there is only 1 God, who is of Three Parts. Just like how you and I are made of three aswell, we were made in His image afterall! Christ was walking in the Garden in that day, Christ is the Body of God. Christ is King, Christ is Truth, He is the Son of God, and He's the Face and Identity of the Invisible God whom created all things. I pray and hope this reaches your heart in some way, or clears any questions. God bless.