Station III
"We may infer a Station I and a Station II. We may conjecture a Station IV." (Station IV is actually the Salt Lions, and Station V is the Grand Geode.)
"Machinery hums behind high steel walls. Up the hill, there are visible outlines of warehouses and a building with a spire. But the lamps are low where they burn at all, and your ship the only one in harbour."
Station III is a top-secret facility owned by a company called Soothe and Cooper. It apparently needs a constant supply of dead bodies to run, specifically the bodies of those who had taken Soothe and Cooper's Heartease Tonic and were killed permanently after overdosing due to a buildup of heartmetal - exactly what it sounds like. (This is why Soothe and Cooper Long-Boxes, aka coffins, are occasionally found in London and around the Unterzee.)
Heartmetal occupies the same legal status as Gaoler's Honey - law-abiding citizens rarely, if ever, speak of it.
