The first adventure in the series starts aboard a ship visiting the Island of St Helena where the Wallace Boys are going to stay with their uncle, the Governor. While on board the RMS St Helena, Bruce discovers that there are a pair of stowaways in one of the lifeboats and he gets thrown off the back of the ship for his pains.When the brothers, together with St Helenian, Jimmy Fowler, arrive on St Helena, they discover that all is not well. Their search for the stowaways, Isaacs and Lambert, who have eluded detection, leads them to Longwood House where Napoleon spent his years on the island following his defeat at the Battle of Waterloo, and thence to the Gates of Chaos, an extremely treacherous part of the island.Matters reach a head when the Governor starts behaving strangely and the three boys find that weapons, including Russian-made AK-47s, have been smuggled onto the island. It is clear that a coup is being planned. Can the boys foil the attempt?