I'm a level 72 Death wizard, and I'm not able to start the Lost Pages event. I have already completed Unicorn's Folly. It's currently July 6th and the event ends on the 15th. When I talk to Harold, I don't get any option to start the quest, I can only buy treasure cards. How can I start this quest?
You have to go to the individual worlds where the Spellwrit mobs created by the Lost Pages are located:
Wizard City Krokotopia Mooshu Celestia Avalon Azteca
You will not be able to start the Lost Pages at any of these locations if you have not already quested to the location in that world where the Spellwrit mobs are. For example, in Azteca you would need to have quested up to the Twin Giants area. In Avalon, you need to have the High Road open.
In Wizard City, you have to talk to Simeon in Ravenwood. He'll send you to Triton Avenue. But if you've already completed his quest in the past, he will not have any quest for you this time. You can check to see if you've done these quests before by looking in your badges section.
In Krokotopia, Sgt. Talbot will send you on to the Grand Arena in the Krokosphinx. In all of these worlds, there's an NPC near the world gate who will tell you about the Spellwrit mobs in that world. Here's a guide that will help you find them.