Special bundled with the Blu-ray/DVD volume of Grisaia no Meikyuu.

The Miracle of Excalibur is the twelfth OVA of the anime and manga franchise Detective Conan. The plot is based on Gosho Aoyama's short story Excalibur. (Source: Detective Conan World)

Diana invites Kogorou and Ran to London, but since Conan cannot travel with his invented name, Ai gives him a temporary antidote, letting him travel as Kudou Shin'ichi. Together with Professor Agasa they are on a plane to London. Back in Japan, Ai now lives with Ayumi. Near their apartment, a suspicious man clothed in black named Kurokawa Youji has been trying to track down and now has found Ai. Shortly after Mitsuhiko notices a picture in a magazine of a foreign actress named Grace Aihara, who looks exactly like Ai, Conan calls, ominously instructing Mitsuhiko to keep Ai away from the Professor's house. And so, Mitsuhiko and Genta go about trying to protect Ai... (Source: foo2)

In this entirely new story produced specifically for the DVD, Conan leads a group of young detectives against the phantom thief Kaitou Kid, who has his eyes set on a jewel at a hotel on an isolated island. (Source: ANN)