Here is my very first puzzle, in the form of several smaller puzzles (around 10, can be changed) linked by a story. Here is the first part, a not-so-small introduction and the first puzzle.
You, a member of a previously rich family, found a few weeks ago a note from your grandfather which talks about a secret hidden inside a jewel. He didn't describe how he did this, but he notes this secret is a transcription of an older secret, discovered by his ancestor and at the origin of their social advancement.
Unfortunately, after his death, all his valuables, probably including this mysterious jewel, had to be sold to pay off a debt. Your research leads you to the probable new owner of this jewel, a paranoid collector only known as "Mr. X" on markets. You only have one clue about him: he never leaves North America. But today, you got a chance to change this.
On one auction site, Mr. X. said he will be present at a party organised by one of his friends to celebrate a new acquisition. This friend invites any people able to find the location of the party. It could be a great occasion to meet Mr. X. You can't pass on this occasion.
The first thing to do is to solve this:
"Two keys are needed to find the solution, hidden in only one sentence. This sentence:
'A right angle is needed in your mind when you'll remember the price of a great betrayal.'
With these keys and what you know about me, you'll be able to find the town of the party."
Where do you need to be to be invited to this party?