Here is Chapter 22 of my fanfic, Nancy Drew: Secrets Can Chill. Today, Nancy solves the endgame puzzles, and I use the word "VHSes" instead of "VHS tapes".
Nancy went to the school library and searched for 5253 on the computer system. There was one result: a book entitled Under My Chair, by Jake Rogers.
Nancy went up the stairs and went to Jake's personal study area, below the periodic table of the elements. Seeing the chart caused Nancy to suddenly realize that Jake's random clues weren't random after all! The things he wrote, like K, Hg and H were all elements!
She reached under Jake's chair and found a metallic box, with many buttons. Nancy soon deduced that she would have to push the buttons in the proper order to get the box open. But what was the proper order?
"I must have to put all the clues together," Nancy said. "I'll put all the elements in order, and match the instructions that came with them, starting with the symbol written on the matchbook from Maxine's and—"
Nancy stopped shortly. That was way too complicated. Instead, she turned around and threw the box down to the first story of the library, where it hit the ground and smashed open.
"All right!" Nancy said. She went downstairs and picked up the box. Inside was another VHS tape.
Nancy took the tape with her back to Aunt Eloise's. She looked around the room for a bit, and wondered why her aunt had a VHS player, but no VHSes. Shrugging, Nancy put the cassette in the player and watched it on the TV.
"Hey, sports fans!" a male voice—obviously Jake's—said. "Guess what our student body president has been up to lately? He's been stealing blueprints and files from his daddy's top secret aerotech company."
Video footage of these things played onscreen, and Jake kept narrating. "What's he been doing with this classified intel? He's selling it to Mitch Dillon, our local HVAC guy. Don't know what a guy like him is doing with government secrets, but hey! Both he and Daryl are willing to pay me a bunch of money to keep quiet."
"Was Jake Rogers blackmailing everyone in Florida?" Nancy asked.
The video cut out for a bit, then came back on. "Hey, great news!" Jake said. "I figured out what Mitch has been doing with the government papers. He's selling them to this loser!"
Onscreen was an image of Detective Beech.
"Yep, now I can blackmail him in addition to Mitch and Daryl," Jake said. "Isn't life great? Better yet, he just left his notebook full of important information at Maxine's. I stole it, and I'm gonna make him pay through the nose to get it back.
"This tape is my insurance policy," Jake said. "It's always good to have plenty of backups, in the blackmail business. But I doubt this guy will give me any trouble. He's probably just gonna give me a ton of cash."
The tape ended there. A few seconds later, the front door to Aunt Eloise's house slammed.
"Aunt...Eloise?" Nancy asked. She walked over to the entranceway. Standing there was Detective Beech.