Sometime before 1237 AE, Henst made a deal with the king of Kryta. If Henst could take over Lion's Arch, King Baede would recognize his authority as a fellow royal and lend him troops and ships to secure the city and drive out all nonhumans. Lion's Arch would become a "new home for displaced Ascalonians", and Henst would be their king.
Henst told Captain Grimjaw to make a bomb to take out Isaye. Macha's job was to put the bomb on the ship, because she could get there without anyone seeing her. Originally, Henst was going to buy a ship and get his own seat on the council, but one vote wouldn't have been enough. So he and Macha came up with a plan.
Henst gave his money to Yomm to buy a seat instead, and then he planned to kill Isaye. Henst was her first mate; he'd inherit her seat on the council. With Isaye dead, Macha could convince Cobiah to leave the city. Henst, Grimjaw, and Yomm could all vote against spending more money on the city's defenses, and once Lion's Arch was unprotected, King Baede's troops would sweep in and declare Henst king of the city.
Henst made Grimjaw a deal. Once Henst took over the city, he'd use Baede's backing to give Grimjaw ships, and Grimjaw would convince the nonhumans leaving Lion's Arch to crew them. He'd get what he wanted—an armada to go attack Orr. Henst also promised to give Grimjaw the Pride, although according to Macha the charr was stupid for believing that he would ever give the Pride up.