|“||In some schools of magic, such as Expression, human sacrifice can be used as a focus for power. It's rumored that the addition of two supernatural sacrifices compounds the mystical energy, creating an Expression Triangle, a rare, but powerful source of magic.||”|
An Expression Triangle is the combination of three brutal massacres that happen at separate equidistant locations. These massacres mark the Earth with power and can be used as focus points for witches who practice Expression. However, focusing this much power causes the weather to become violent, creating windstorms and thunderstorms, and causing power outages in the area encompassing the triangle.
Now, upon activating the final focus point using Expression, the witch in question can then begin to channel the immense mystical energy from these three locations. In Bonnie's case, she was being coerced by Professor Shane, who in turn was being manipulated by Silas, to complete the Expression Triangle and to channel its three focus points to perform a powerful spell. This powerful spell was part of Silas' goal to nullify the Other Side, via dropping the Veil, which separates the supernatural purgatory from the physical world. Dropping the veil to the Other Side would essentially allow every deceased supernatural creature to return to the land of the living.
Qetsiyah, the ancient witch who created both the Immortality Spell and the Cure for immortality, and who buried the first immortal Silas, had also created the Other Side, a purgatory for all supernatural creatures to be trapped after their death. When she buried Silas with the Cure, she had hoped he would take it and die of old age, which would result in him being sent to the Other Side and keep him from reuniting with his human true love, Amara, in the Afterlife. Silas refused to let this happen, so he let himself desiccate in tomb for over two millennia, only being fed dribbles of blood by travelers who allowed to drip their blood into the well over his tomb and waiting for a chance to be freed.
Silas' chance came when Atticus Shane, a man who had lost both his wife Caitlin and his young son, went in search of a well where rumor had it you could see your deceased loved ones if you dripped your blood into it. Unknown to him at the time, Silas was buried there, and the "ghosts" you could see from bleeding into the well were actually hallucinations Silas had created with his powerful psychic abilities after establishing a connection by the blood dripped into his mouth. Using a vision of Shane's wife, Silas manipulated Shane into finding the means to free him. He also manipulated Shane into starting to prepare the sacrifices Silas would need to make an Expression Triangle so he could permanently take down the veil that separated the living world from the Other Side, thus allowing every deceased supernatural who had died since its creation to return from the dead.
The first sacrifice of twelve was performed by killing twelve members of the newly-reformed Town Council. After his own wife's passing, Pastor Young was stricken with grief and Shane became a kind of therapist for him, helping him get through his loss. Little did Young know that he was being manipulated and hypnotized by Shane.
At the end of the day that Pastor Young had attempted to rid Mystic Falls of vampires, Shane had him trap himself and the other eleven members of the Council in his house, where he had filled the room with natural gas from the oven before lighting a lighter, which caused all twelve people to perish in the resulting explosion. This marked the first sacrifice of three to create the Expression Triangle.
Meanwhile, Shane began paving the way to release Silas, calling upon the help of the Brotherhood of the Five and their Hunter's Marks, which would be used in unearthing the immortal. He also befriended and became a mentor to Bonnie, whom he began to teach Expression, knowing he'd need her to use the branch of Dark Magic to both free Silas and utilize the Expression Triangle.
- Main article: The Sacrifice of Twelve Hybrids
Knowing he'd need to sacrifice another twelve lives, and in this particular sacrifice, twelve "demons," Shane came into contact with a werewolf named Hayley. He knew Hayley's parents had died, so he took advantage of her grief, much like he did Pastor Young's, and promised her he would help her find her parents if she helped him. He got her to tell him about her experience with the hybrid, Tyler Lockwood, who she had helped in breaking his sire bond to the Original, Klaus, which every hybrid sired by Klaus experienced. Since the Supernatural Hunter, Connor Jordan, had found Tyler in Mystic Falls during Shane's plan to make his Hunter's Mark grow, Shane knew to send Hayley to Mystic Falls to find her old friend.
Shane had Hayley convince Tyler that the other hybrids needed to break their sire bonds and rebel against Klaus, though, Shane and Hayley knew that this would never work, and were really planning to give Klaus a reason to kill twelve of his hybrids. Their plan went smoothly, with Hayley getting Tyler to believe that they were starting a necessary revolution against Klaus by having the hybrids break their bonds. However, it was all a manipulation on the part of Shane, and by association, Hayley, and once the hybrids had broken their bonds, she informed Klaus of this before fleeing town. Klaus found the hybrids and relentlessly killed them all, butchering them with his Alexander's sword. These twelve deaths marked the Earth with the second part of the Expression Triangle.
- Main article: The Sacrifice of Twelve Witches
Still under the visage of Atticus Shane, Silas continued his quest to complete the Expression Triangle, stealing blood in order to feed after two millennia of desiccation. He kept Bonnie under his control, reminding her that she could bring back her deceased loved ones with the Expression Triangle's help, such as Jeremy and her Grams. With her finally on-board to complete the final sacrifice, Silas explained that the third sacrifice required a massacre of twelve witches. Bonnie grew hesitant at the thought of killing a dozen members of her own people, but Silas reminded her that they'd be brought back to life once they brought down the Veil to the Other Side. He told her that the witches would all link together with spirit magic to try and help remove the Expression from her being, and was instructed to fight against them until they had linked before finally killing them all.
Bonnie contacted a friend of her mother's, Aja, under the guise of asking for her help in cleansing her of Expression. Aja brought her whole coven of witches to help with the spell. They began the spell and eventually linked together when Bonnie proved to be too strong, channeling all their magic into Aja, who tried to save Bonnie. However, Caroline, Stefan, and Klaus had realized what Silas and Bonnie were planning and were intent to stop the third sacrifice from happening. When Stefan finally found the witches and told Aja that Bonnie was under Silas' control, Aja determined that Bonnie was beyond their help. Instead, she started praying to the spirits to save her soul before pulling out a knife to kill her. Not wanting to complete the triangle, but also not wanting her best friend to be killed, Caroline ultimately decided to kill Aja, who was linked to the rest of her coven, and which resulted in the death of all twelve witches, finally completing the Expression Triangle.
However, upon awakening from the witches' attempt to cleanse her of Expression, Bonnie remembered nothing beyond the point that she and Jeremy found Silas and the cure in his tomb. After this sacrifice, Silas had everything he needed to achieve his goal, except for the Cure, which he wished to take before killing himself so he could reunite with Amara after Bonnie brought down the Veil to the Other Side with the fully charged Expression Triangle.
Originally believed by Silas that Bonnie would draw on the power of the full moon to activate the triangle and drop the Veil, she actually planned on using Silas' Tombstone, which contained the calcified blood of Qetsiyah, an equally powerful source of magic. Beginning the spell a night earlier than expected, she drew on the power of the tombstone and the sacrifices to drop the Veil, but only temporarily and only within the borders of the triangle. Bonnie didn't want the Other Side to be gone for good - she only wanted to speak with Qetsiyah to learn how to finally defeat Silas. When Bonnie dropped the Veil using the triangle, ghosts were able to roam free within the boundaries of the triangle and had access to all of their powers prior to death; however, if they stepped outside the bounds of the triangle, they were sent back to the Other Side.
Releasing Silas became top priority before the third and final sacrifice could be completed. Shane continued to teach Bonnie how to use Expression, even though he knew it had the potential to be too powerful for her to control. He also had convinced Jeremy Gilbert, a new member of the Five, to begin to complete his Hunter's Mark by killing vampires after Connor Jordan was killed. The spell on the Hunter's Mark would be used by Bonnie to open Silas' tomb. Things grew complicated, however, when the Original Vampire, Kol, who had a great fear of Silas, caught on to Shane's plan. He nearly killed Shane, and then set out on trying to kill anyone who was searching for the Cure, since that would also force them to release Silas. Luckily for Shane, Jeremy killed Kol, which killed all of the vampires in Kol's bloodline, causing the Hunter's Mark to finally complete itself after the deaths of an unknown (but presumably large) number of vampires sired by him. Having everything he needed; a hunter with a completed mark, a Bennett witch who could use Expression, and the knowledge of the location of the island where Silas was buried, Shane set off to complete the next part of his plan. He brought a group of vampires with himself, Bonnie, and Jeremy, to the Island under the guise of finding the cure for them. He quickly betrayed the vampires on the island, though, in order to get a head start and release Silas. He brought Jeremy and Bonnie to Silas' tomb, where he had Bonnie use Expression to perform the spell on Jeremy's Hunter's Mark which caused a collapse in the cave that trapped Shane under a piece of rock and broke his leg.
Silas could feel that they were close, though, and used his connection to Bonnie through her blood to create hallucinations of her Grams that would draw them to him. Bonnie and Jeremy found Silas' fossilized body and discovered the cure, of which there was only one dose, clutched in his desiccated hands. Katherine Pierce appeared, pretending to be Elena and having her own reasons for wanting the cure, and fed Jeremy to Silas, which awakened the immortal and led to Jeremy's death at Silas' hands while Katherine departed with the cure. Silas took the form of Shane and brought Bonnie back outside onto the island, pretending to be her mentor Shane and using an unknown means to heal her of her wounds.
He told her all about how the sacrifices were the means to create an Expression Triangle, which she would then use to channel the power which would allow her to lower the veil to the Other Side and essentially merge the dimension with the living world, freeing all of the souls within it, which included Jeremy and other loved ones, but also countless dangerous vampires, hybrids, and witches that the Mystic Falls Gang had eliminated. Silas managed to convince her to go along with his plan, using a hallucination of Jeremy pleading for help which ultimately caused Bonnie to accept her responsibility of completing the third sacrifice.
- The Expression Triangle is responsible for marking Mystic Falls with power.
- It is interesting that each sacrifice occurred 8 episodes apart; Growing Pains (humans), O Come, All Ye Faithful (hybrids), and Because the Night (witches).