Each card has a letter and a number in the bottom left corner. You will have noticed that one specific card has a decoder where letters and numbers can be unscrambled. In fact, you used this decoder to remember the security code that I sent you.

If you decode all these letters and numbers you will have a series of other letters and numbers. Here's the solution: The letters form a sentence, and their numbers define the position of the letter in that sentence.

— Q