A docking accident has thrown the transport system that the space settlement of Liwan depends on into crisis.
Engineer Lu Heng is ordered to find the cause, only to discover that gravitational anomalies along the route seem to be responding to human actions.
There are no signals, no language, and no visitors anyone can see. To test this response, he and researcher Wen Lan can only move enormous counterweights, using mass and gravity to try asking questions of the darkness.
But Liwan cannot afford to wait. Cargo ships are already on their way, supplies must keep flowing, and humanity's ever-expanding transport network may have intruded on the very place where another kind of being survives.
When restoring traffic and stopping the harm cannot both be achieved, Lu Heng must decide whether to dismantle with his own hands the System he helped build, and clear a path for a neighbor whose existence has yet to be confirmed.
Every test comes at a cost to someone. Before the next response arrives, they must make their choice.
