|... And the Dark Secret|
|Directed by||Marc Roskin|
|Written by||Marco Schnabel|
|Original airdate||December 13, 2017|
|Previous Episode||"...And the Wrath of Chaos"|
|Next Episode||"... And the Steal of Fortune"|
When a secret sect of the Vatican Church unearths an ancient map detailing the locations of the four cornerstones of the Library of Alexandria (the original Library), it’s up to Flynn and the Librarians – with the help of an unexpected ally – to stop them before the stones can be used to destroy the Library.
A group of priests are hunting down the four cornerstones of the Library of Alexandria, not caring if they have to kill in order to accomplish their goal. They find the first in a church and the second in a barrel displays at a park.
The Librarians are rehearsing a ceremony that will bond Flynn and Eve to one another as well as tether them to the Library. The ritual is important to ensure the safety and lasting power of the Library. The Librarians get word about the cornerstones being taken so Ezekiel, Jacob, and Cassandra set out to the park. Ezekiel swipes a memory card from a tourist photographer and finds images of the priests on it. They must find the other cornerstones or else the Library can be destroyed forever.
Back at the Library, Nicole Noone is found. Nicole was Flynn's original guardian and has been locked up in a secret part of the library for hundreds of years. She is immortal and was formerly romantically involved with Flynn. She is the one that hid the cornerstones and Flynn had long believed her to be dead. She will talk but only to Flynn.
The group gathers at the Library again while Flynn speaks to Nicole. Jenkins tells the others that the heretic Order of Shadows are responsible for what's going on, when he recognises the design of flames in their cross. They want to destroy the Library so that they will destroy all the knowledge and enlightenment it brings to the world.
Jacob determines that Nicole came up with a pneumonic device related to the muses that allowed her to remember where she hid the cornerstones. This allows the team to figure out where the final cornerstones are hidden. Jacob, Ezekiel, and Cassandra head to the Paris opera house. Cassandra calculates that the three of them need to sing a High C to shatter the crystal that has blocked off the cornerstone. They retrieve it and the priests emerge to try to capture it for themselves. A chase ensues while some opera singers rehearse. The trio is caught and brought into a car where they meet the leader of the Order of Shadows, Monsignor Vega (John Noble).
Eve demands that Nicole be released so she can take them to the final cornerstone. They head to a lake with Flynn and are met with considerable amounts of lightening shooting off. Nicole won't got into the field to retrieve it herself due to the lightening that keeps shooting into the ground. Flynn shoots mineral samples into the air to maneuver the lightening away so Eve can reach the stone. Once she gets there, the other two follow and retrieve it together. They are distracted by the sound of Cassandra screaming. When they all run into the barn they find the Order of Shadows and the other three Librarians. With all four cornerstones, they're able to start the ritual to try to destroy the Library.
The Librarians begin to fight the Order. Nicole uses one of the cornerstones to distract Monsignor Vega and throws it into the centre of the vortex created. Without the power from the fourth stone, the vortex is at risk of collapsing. Monsignor Vega has been sucked in and Nicole by accident. Flynn insists on jumping in after her. Cassandra figures out how the Librarians and Eve can boost the signal and they all work together to keep it open long enough for Flynn to retrieve Nicole and the Library is saved.
Eve calls in a favor to have the members of the Order arrested. Nicole runs off while the Librarians and Eve are celebrating. Nicole only stopped the plan to destroy the Library because she wanted to save Flynn. The team contemplates whether Nicole will pose a threat to them and the Library's safety in the future before resuming rehearsals for the ceremony that they only have three months to perfect before the vernal equinox on which it must take place. Flynn admits to Eve that he is worried about the ethical issues with Nicole's captivity but she assures him that an institution is only as good as those that run it and together they can make it something upstanding. Finally, Flynn finds a book left for him by Nicole that holds a picture of the two of them from younger days.
- Rebecca Romijn as Eve Baird
- Christian Kane as Jacob Stone
- Lindy Booth as Cassandra Cillian
- John Kim as Ezekiel Jones
- John Larroquette as Jenkins
- John Noble as Monsignor Vega
- German Santiago (as German Alexander) as Father Giallo
- Lex Damis as Priest #2
- Nathan Crosby as Park Ranger
- Tim Harrold as Cop
- Tommy Daniels as Priest #1
- Barbie Wu as Photographer
- Ciro Fusco as Old Italian Worker