Two Halves

Shen Yuan has a red mark on his palm, a key implanted by a dying pilot. Lin Nian has a mark on her wrist, a code left by her mother on the far side of the Moon. On the winter solstice night, both halves of the key activate simultaneously, shattering the thirty-year silence between Earth and the Moon. But the Moon people have already arrived. The secret of Ark Division was never truly sunk—it was merely split in two, hidden in the cracks between two worlds. Now two young people must find a way to survive between the war faction and the moderate faction, and recover the other half before it's too late. — Description from novelcodex.org