In early 1908, Hoang Hoa Tham collaborated with Vietnamese nationalists, including Phan Boi Chau, in organizing a plot to seize Hanoi from the French.
Vietnamese cooks were to neutralize the French garrison in Hanoi by poisoning their dinner foods; at the same time, Vietnamese soldiers (Grade Indochinois) would attack and prevent French troops at Don Thuy, Son Tay, and Bac Ninh from coming to the aid of the Citadel of Hanoi; and Hoang Hoa Tham would wait outside the citadel and launch an attack on Gia Lam when the signal arrived from the inside.
[1] The plan was executed on the evening of 27 June 1908, when the group of Vietnamese cooks managed to mix datura poison with food they had prepared for a party.
Dronet Ân) then reported this to government officials;[2] the French general-in-charge in Hanoi immediately proclaimed martial law and ordered the arrest of plot leaders and plotters.
[1] Severely repressive actions[clarification needed] were launched against the Vietnamese activists, and hundreds of them, including Phan Châu Trinh, were sent to Con Dao prison.