Five teenagers from the Bronx, along with the younger sister of one, set out to explore a cave in a wooded section of their neighborhood. The cave exploration is a washout. A section of the cave floor collapsed - and that was the major event of the trip! Disappointed, hungry and tired, the six start the return trip home, only to find that "home" has vanished.
They are still in the Bronx, but they have time-traveled two or three centuries into the future. Here, the Bronx is a heavily-wooded forest, unexplored by the tribe of people living there. After saving the life of one member of the tribe, the Bronx teenagers are accepted and slip easily into village life. Within weeks however, they find themselves in the middle of a fight for survival.
Another tribe living in Manhattan is bent on wiping out the tribe in the Bronx!
These teenagers have a unique advantage in this war. They know the land. Neither tribe is aware that there were and still are, train tunnels running under the river from the Bronx to Manhattan. Neither knew that the old train tracks ran North/South so are excellent travel guides. The tribe in the Bronx is even unaware of the wealth of treasure - metals, jewelry, etc. - buried in the rubble of what were once busy shopping strips in the Bronx. For the six, this becomes a true adventure. They are able to help their friends, and outsmart the enemy.
However, all too soon their adventure becomes very real. First their dog dies, and then one teenager gets wounded. Now both friends and enemies are getting killed. This was no longer fun! This was a fight for survival!