Boris was excessively alarmed.  With characteristic energy he speedily raised an army of two hundred thousand men, and then was in the utmost terror lest this very army should pass over to the ranks of his foes.  He applied to Sweden and to Denmark to help him, but both kingdoms refused.  Dmitri advanced triumphantly, and laid siege to Novgorod on the 21st of December, 1605.  For five months the war continued with varying success.  Boris made every attempt to secure the assassination of Griska, but the wary chieftain was on his guard, and all such endeavors were frustrated.  Griska at length decided to resort to the same weapons.  An officer was sent to the Kremlin with a feigned account of a victory obtained over the troops of Dmitri.  This officer succeeded in mingling poison with the food of Boris.  The drug was so deadly that the usurper dropped and expired almost without a struggle and without a groan.

As soon as Boris was dead, his widow, a woman of great ambition and energy, lost not an hour in proclaiming the succession of her son, Feodor.  The officers of the army were promptly summoned to take the oath of allegiance to the new sovereign.  Feodor was but fifteen years of age, a thoroughly spoilt boy, proud, domineering, selfish and cruel.  There was now a revolt in the army of the late tzar.  Several of the officers embraced the cause of Griska, declaring their full conviction that he was the Prince Dmitri, and, they carried over to his ranks a large body of the soldiers.

The defection of the army caused great consternation at court.  The courtiers, eager to secure the favor of the prince whose star was so evidently in the ascendant, at once abandoned the hapless Feodor and his enraged mother; and the halls of the Kremlin and the streets of Moscow were soon resounding with the name of Dmitri.  A proclamation was published declaring general amnesty, and rich rewards to all who should recognize and support the rights of their legitimate prince, but that his opponents must expect no mercy.  The populace immediately rose in revolt against Feodor.  They assailed the Kremlin.  In a resistless inundation they forced its gates, seized the young tzar, with his mother, sister and other relatives, and hurried them all to prison.

Dmitri was at Thula when he received intelligence of this revolution.  He immediately sent an officer, Basilius Galitzan, to Moscow to receive the oath of fidelity of the city, and, at the same time, he diabolically sent an assassin, one Ivan Bogdanoff, with orders to strangle Feodor and his mother in the prison, but with directions not to hurt his sister.  Bogdanoff reluctantly executed his mission.  On the 15th of July, 1605, Dmitri made his triumphal entry into Moscow.  He was received with all the noisy demonstrations of public rejoicing, and, on the 29th of July, was crowned, with extraordinary grandeur, Emperor of all the Russias.