Summary: David escaped to the Caves of Adullam where he became the leader to around 400 men with different troubles who had heard that he was hiding there. David arranged for his parents to stay with the King of Moav and progressed to the Forest of Cheret. Shaul demanded loyalty from his men.
A deeper look: Doeg Ha’Adomi (Doeg the Edomite) revealed that he had witnessed Achimelech provide David with food and armament (Samuel I 21:8). Shaul assumed that this had been an act of treachery against him and summoned for Achimelech. He ordered his men to kill Achimelech and his entire household. The men refused Shaul’s order and so on Shaul’s command, Doeg proceeded to kill 85 Kohanim and massacred every man, woman and child of the city Nov. Eviyatar, one of the sons of Achimelech escaped and informed David.
Although Doeg was Jewish, he lived in the area of Edom and was therefore called Ha’Adomi, the Edomite. Edom (meaning red) is the nation who descended from Esau and refers to the red lentil soup which he took from Jacob in exchange for his birthright (Genesis 25:30). The name Edom also points to the nature of Esau as a ‘spillers of blood’ (Rashi on Genesis 25:25) and they became an eponymous enemy of the Jewish people.
Rabbi Shimon Ashkenazi HaDarshan of Frankfurt (c. 1260) cites midrashic sources which associate Doeg with the nature of Edom, for shedding the blood of so many innocent Kohanim. He turned David and his wife into fugitives making it acceptable for others to kill them. He is credited with being the one who persuaded Shaul to spare the life of Agag (Samuel I 15:8). He would also regularly embarrass people which the Gemara (Bava Metzia 58b) likens to murder (Yalkut Shimoni 131).
The Chofetz Chaim (d. 1933) cites this incident as an example of what can happen when someone engages in rechilut (tale bearing) and lashon hara (evil speech). Doeg knew that Achimelech had acted out of loyalty to Shaul, not treachery. He had given David provisions because he thought that he was on a mission from Shaul. Yet Doeg only told part of the story to create a narrative of betrayal. He therefore curried favour with the king by demonstrating his own loyalty (Samuel I 21:3). Yet the result was a national tragedy. Indeed, the Gemara cites Doeg as one who lost his share in the World to Come (Sanhedrin 90a).