Merlin's Diary

From Tardis Wiki, the free Doctor Who reference
Merlin's Diary held by Merlin himself. (COMIC: Dr. Who's Time Tales)

Merlin's Diary was the title of a large leather-bound book that contained some of Merlin's magic.

It remained in Merlin's possession until the 20th century. When he carelessly left it in a public area of the curiosity shop in the Balkans where he had come to reside, an American businessman tried to buy it, not believing his warning that the book was dangerous and best unopened. After he opened the book, a spell sent the American back in time to the Middle Ages, where he meant Merlin in his prime before being sent back to the "present". After he left the shop, frightened and shaken to the core, the modern-day Merlin resolved to better hide his diary in the future. (COMIC: Dr. Who's Time Tales)