This article is associated with Into the Gauntlet.
"The Cahills have made groundbreaking scientific advancements, discovered new lands and explored the most perilous places on Earth in pursuit of the Clues. However one secret remained hidden: the formula Gideon Cahill's master serum--the key to assembling the Clues. After over 500 years of bloodshed and betrayal, Amy and Dan located the Madrigal stronghold and discovered the most valuable Clue of all: the serum formula. Although they destroyed the formula, to keep the serum from Isabel Kabra, Dan was able to memorize it. The hunt was over, but the dangerous information remained in Dan's head."
The entire Serum formula, detailing its ingredients and instructions for its production. Gideon Cahill created the first version of the Serum in 1507. It's purpose was to cure plague, though it also amplified several characteristics of the imbiber, namely physical strength, artistic talent, mental ingenuity, and swift cunning. It was, however, imperfect in that it was eventually fatal to the imbiber. When Gideon learned of this, he split the Serum formula into four parts and distributed them among his children. He later died, and his children parted ways. His daughter, Madeleine, later created her own version of the Serum Formula to offset the fatal tendencies of the Serum.
In the official contest for the 39 Clues, Isabel Kabra learned of the Serum formula, subsequently created the Serum, and nearly drank it, but the combined efforts of several branches of the Cahill family foiled her, destroying the Serum in the process. She was not able to memorize the formula, but Daniel Cahill did so unintentionally with his photographic memory.
In their later struggle against the Vespers, Dan painstakingly recreated the formula, eventually creating two samples of the Serum, one of which was destroyed by his sister Amy Cahill. The remaining Serum was later stolen by Isabel Kabra, who drank it once she saw that her daughter Natalie had been killed by the Vespers. The Serum worked as it should have, aside from giving her a red pallor due to Dan's additon of red M&M's to the Serum "to give it flavor". With the new talents at her disposal, she was quickly able to eliminate the Vespers and destroy the Doomsday Device, though she was killed in the process. As of yet, no known Serum or any copy of its formula exists, and the knowledge to make either is to be found only in Dan's memory.
The screen shows a cave, with a little light showing the Master Serum, a flask with green liquid and a Cahill crest on the flask. The flask spins quickly and reveals the ingredients of the Serum. It keeps spinning until it flashes and reveals the black screen with the word 'SERUM FORMULA'
- The Serum Formula is the formula for combining the other 38 Clues into the original Master Serum Gideon discovered. It is as follows:
One portion = one ounce
Start with one portion of water.
The unknown part of the Serum Formula consists of the amount of Ekaterina, Tomas, and Madrigal Clues to add. The portions for each talented branch were based on the pattern of fractions, either going down by half each time, or by each eighth portion. 1/64 of a portion is way too small to calculate, even with high-tech instruments, so it is safe to say that it is by the eighth of a portion. The Madrigal portion was determined by the average of each portion, causing a balance in the ingredients. Although this has not yet been tested by any willing Cahill, this is likely how it goes.
The Master Serum can be created if someone has the Serum Formula and all of the other 39 Clues. The Master Serum is fatal to theits imbiber without the balancing ingredients that comprise Madrigal Serum. Without them, the Serum is deadly, slowly deteriorating your health at your each use of the skills it granted you. It may be possible to obtain the skills provided by the Serum by making each branch's Serum individually. You might not need the Madrigal Serum, but it would take longer to make and use.