This page contains spoilers for the following products: Silent Tide (scenario).
The original plan involved a secret group of secret agents known as the Black Echelon weakening defenses within the city itself during the foggy month of Desnus. Once Absalom was in a more vulnerable state, a series of signals were to be given, bringing with them a naval attack from a giant armada which had been waiting off the coast of the Isle of Kortos. Most of these signals would involve colored lights from high buildings for internal Black Echelon operatives, but the final signal was the interruption of the Oathday playing of the great organ in the Metro-Cathedral. When the decided date came, no signals were given; the operatives had been discovered and their sinister plan was foiled. It wasn't long before Absalom's navy overtook the waiting Taldan fleet, ending the threat and stopping the Silent Tide before it began.
The members of the Black Echelon hunted down and put to the sword, no one Absalom thought any more of the Silent Tide. There was one piece of information they were missing, however. Prior to the operation's onset, each member of the Black Echelon cell swore the Binding Word, an ancient oath that held them to their mission even beyond the grave. For centuries these operatives lay in wait for the decided-upon signals.
In 4708 AR an elderly military historian named Yargos Gill came into possession of the Black Echelon's codebook and unwittingly began the Silent Tide almost a millennium after it was intended to go off. When the codebook was then stolen from him by the War Hounders gang and their leader Nessian, it fell to the Pathfinder Society to end the threat of undead saboteurs and a long sunken armada of ghostly invaders to the city of Absalom.