Fail-safe diamond

"Like a self-destruct button. Like you never did it?"

- Henry Mills

The fail-safe diamond is a magical jewel that, when pierced by a dwarf's pickaxe, reverts the town of Storybrooke, Maine into the forest it once was and kills any its other-worldly residents within. It was created by Queen Regina when she cast the Dark Curse to be used as a last resort should she find herself having to undo what she started.

Season 2
Regina finds Henry and shows her the magic beans. She explains that his family wants to take him to the Enchanted Forest and leave Regina behind, and that they don't see the good in her that Henry has seen. Regina insists that she wants to go back and start over as a hero, and explains that there's a failsafe built into the curse. With it she can reset time, making Storybrooke disappear. Regina says that they'll get away to the Enchanted Forest first using the beans, but everyone else will die. Henry tells her that she's a villain if she's willing to kill everyone, and vows to stop her. Regina casts a spell making him forget what she just said. Later, Hook and Regina go to the library and descend into the tunnels beneath Storybrooke. Regina notices that Hook has the cuff that Cora gave him to climb the beanstalk. She demands it back and Hook reluctantly turns it over. Regina then leads him on to the dragon's lair where she has hidden the curse's failsafe. When he wonders who is guarding it, Regina says that it's an old friend and that she needs Hook's help to keep the sentry distracted. She then shoves him into the cavern below and Maleficent's undead corpse appears and attacks Hook. Regina makes her way to Snow White's glass coffin and shatters it. She removes the fail-safe diamond within and studies it carefully. When Regina returns to the library, she finds Hook waiting for her. Tamara and Greg appear: they saved Hook and activated the mechanism they placed within the bracelet rendering Regina's magic useless. They kidnap her and Tamara steals the fail-safe from her.

At the docks, Tamara meets with Greg and shows him the beans that she took from Regina's office. When Greg is jealous that she's with Neal, Tamara assures him that she'll be with him when it's all over. He gives her the jewel that Regina took from the coffin, but neither one of them knows what it is. Tamara decides to send it back to the home office, along with everything else. After Neal's "death", Emma wonders how she's going tell Henry, but David doesn't have an answer for her. Meanwhile, Regina wakes up and is shocked to learn that they saved her. David tells her that despite their differences, they're family. When Regina learns that Greg and Tamara got away, she tells David and Mary Margaret that they still have the failsafe trigger. Tamara finds Greg at the campsite, where his father is buried, and gives him the gem. She has checked with the home office and confirmed what the gem will do. Regina tells David and Mary Margaret about the failsafe trigger, and points out that they were going to abandon her. However, she tells them to focus on the fact that their enemies have the trigger. Tamara tells Greg that the home office wants them to use the trigger and destroy Storybrooke.

Greg, Tamara, and Hook enter the mines. They find a dwarf's pick axe and prepare to break the trigger. They tell Hook that it will revert the town to the original forest killing everyone, including Rumplestiltskin. When Greg hits the trigger gem, it floats into the air and starts glowing. The trio runs out as the ground stars to shake. Emma and her parents take Henry back to their apartment, where Regina is getting up after her ordeal. The building shakes and Regina warns them that the trigger is active. Henry wonders if they're all going to die and Regina assures him that he will survive, since he was born there. Hook comes in and offers to lead David to Greg and Tamara while Emma goes with Regina to slow down the trigger. In the mines, Emma and Regina find the gem and the Queen warns that once it stops glowing, it will destroy Storybrooke. She prepares to contain the energy but warns Emma that it will kill her. Regina says that it's fitting that she dies trying to stop the device she created. Crying, she asks Emma to let her die as Regina rather than the Evil Queen and then begins containing the trigger. Later, Regina warns Emma, Mary Margaret, David and Henry that she can't contain the trigger much longer. Emma gets an idea and says that perhaps together they are strong enough. David and Mary Margaret get Henry to cover while Emma joins her magical efforts to Regina. There's an explosion and the gem drops to the ground.