(from ebookjapan):

The group "Silver" is a group of five former Olympic athletes, led by a knife master, and a strong and talented marksman.

Their mission this time was to retrieve the ship Dolphin, which had gone missing after three hours of radio silence after setting sail.

They rescued the crew of the Dolphin, which was afloat at sea, but they were "hijacked by a dog, the White Wolf Maru," they said, and they held their breath.