As Harry sat there after using his Patronus Charm to save his and Dudley's life, an ancient being showed up, it looked like a dementor so he pulled up his wand and was about to cast the spell again but the being looked at him and said "that will not work on me."
Harry looks at it and asks "what are you?" because he now knows it's not a dementor, because dementors can't talk.
The ancient being looks at him and says "I am here for this one's soul" while pointing at Dudley's body, " he has died of a heart attack and in case you are wondering I am Death."
Harry turns deathly pale at that statement.
Death looks over at him and says "I see you have my original cloak. If you give it to me I will give you a different one."
Harry looks at Death and asks him "what do you mean by your original cloak."
Death looks at him and says "the Invisibility Cloak that has been passed down in the Potter family is my cloak that I gave to one of the Peverell brothers. It along with the Elder Wand and the Resurrection Stone are what you wizards call the deathly hallows."
When Harry hears this he asks "What are the deathly hallows?"
Death looks at him and says "the hallows by wizard standards say that if you bring all three of them together you would become known as the Master of Death. However this is not true, if anyone besides me were to have all three of the hallows at the same time, it would automatically kill them and send them to me."
Harry then asks "so if I give you this cloak you'll give me a different one?"
Death looks at him and says "yes, I call it the Cloak of Shadows, what it does is it lets you travel in the shadow realm, while in the shadow realm you will be invisible to all beings, you will be able to see and hear everything but they will not hear or see you. It gives you many more abilities than just invisibility, it allows you to shadow walk between different shadows, if you are thinking about someone you can teleport straight into their shadow, if you touch anything or anyone you can bring it or them into the shadow realm. There are other abilities but I will let you figure them out as you go."
Harry stared at Death thinking about it and figured it would be better for him to have the new cloak, so that way no one would die if they accidentally had all three hallows. So he looked at Death and said while pulling out the invisibility cloak "here's the cloak."
Death grabbed the cloak and put it on, then grabbed a different one and put it into Harry's soul. Then looks over at him and says "good luck."