Judges introduces most of its judges at the moment a crisis calls them forward. Deborah is introduced differently: the text finds her already sitting in judgment, under a palm tree that bears her name between Ramah and Bethel, and Israelites are already coming to her to have disputes settled, before any mention of Sisera or the twenty years of Canaanite oppression the chapter is about to describe. She is a judge in the ordinary sense, settling cases, before she becomes a judge in the military sense the book usually means by the word.
The military crisis is specific: Jabin, a Canaanite king reigning at Hazor, has oppressed Israel for twenty years through his commander Sisera, whose nine hundred iron chariots have made open battle unthinkable for the Israelite tribes. Deborah summons Barak son of Abinoam from Kedesh in Naphtali and delivers what she frames as a direct command from Israel's God: gather ten thousand men from Naphtali and Zebulun, march to Mount Tabor, and God will draw Sisera's army to the Wadi Kishon and deliver it into Israel's hand. Barak agrees on one condition, that Deborah go with him; she agrees, but tells him the campaign will bring him no glory, because God will sell Sisera into the hand of a woman.
That woman is Jael, wife of Heber the Kenite, in whose tent the fleeing Sisera takes refuge and asks for water; she gives him milk instead, waits for him to sleep, and drives a tent peg through his temple. The battle, fought in a downpour that mires Sisera's chariots in the swollen Kishon, is recounted twice, once in the prose of chapter 4 and again in the poem of chapter 5, and the two accounts do not agree on every detail, a divergence the next article takes up directly.