Tesla's Mystery

Nikola Tesla was one of the greatest scientists who have ever lived. Up until his death in 1943, he invented over 300 patents, some of which being invaluable to humanity, setting the foundation for the world we know today. Just before he died, he wrote a letter to some of his loyal friends, telling them that he has invented a real teleportation device. In the letter, he expresses concern that the sketches for that invention may fall into the wrong hands of government agents or foreign spies who will use them for military purposes. So, he asks his friends to meet him at his apartment in the New Yorker hotel so he can give them the blueprints. As soon as they arrive they find out that Tesla died in the meantime, but he was clever enough to hide the blueprints well and leave some clues which only they would be able to figure out.