Rainy Afternoons Are Dangerous!

One rainy afternoon, a man seeks Lupin's help on behalf of a young woman. The young woman turns out to be Fujiko who is naturally after a piece of jewelry.
This is no ordinary piece of jewelry though. The Star of Killamanjaro diamond was implanted into the chest of a mob boss. This boss had his memory wiped but died days before it was to be restored. Now, Lupin and the gang are after the ambulance carrying the corpse and the diamond in it.
Naturally, Zenigata is in charge of the ambulance and its escort. Who will get to the diamond first?