The Cutie Mark Crusaders, frustrated with their lack of success, begin searching through Twilight's library in an attempt to find out more information about cutie marks themselves in the hope that they will finally understand the way to get their cutie marks. However, the trio runs across an ancient book containing evil spells and they attempt to get their cutie marks in the worst way possible...
Cover art by http://sniper-bait.deviantart.com/

Now with its own TV Tropes page! http://tvtropes.org/pmwiki/pmwiki.php/FanFic/TheCutieMarkCrusadersBringAboutTheApocalypse

Twilight Sparkle and her fellow Elements of Harmony have faced down supernatural foes of the highest order, but sometimes the deadliest danger can come from places one would least expect. As Twilight is forced to bear a devastating secret, her efforts to keep the Elements together may well tear them all apart.
The plotline of the thrilling Pony Psychology Series continues with an exploration of deception, despair and Discord.
This series takes place between Season Two and Season Three.
Secrets and Lies shares the Pony Psychology Series TVTropes page.