1141 was a turbulent year in England's history. The Civil war had reached an early deadlock, dramatically broken by the capture of the king at the Battle of Lincoln, and the defeat of the Empress at Winchester.
Stephen had serious hacked Ranulf off by giving Carlisle to David King of Scots. He'd granted Lincoln in compensation, but demanded a Royal garrison. Plus, Stephen had built up the power of the Beaumonts, just as a counter- weight to any defection from Ranulf. So in 1141, Ranulf seized Lincoln, and joined the Empress.
The defection made a big change to the Angevin's fortunes – in reality they'd been very disappointed by the number of Barons that had joined their cause. Ranulf gave them a vast block of land in the North West.
The Battle of Lincoln, 2nd February 1141
Lincoln is the only straightforward pitched battle of the Anarchy. And if Stephen had more of a brain there wouldn't have been any battles at all. The Angevin party, accompanied by a large contigent of Welsh with Ranulf, was probably considerably larger than Stephen's army. He should have withdrawn. But maybe spurred on by the memory of his father's disgrace, he decided to stay and fight. Despite some early success as the royal cavalry routed the Welsh on the wings, the Angevin counter attack drove the king's supporters from the field. Still Stephen refused to fly, was surrounded and after figjhting bravely was over whlemed and captured.
Matilda Fluffs it.
This was Matilda's big chance. Most barons accept that she's now in control, Henry of Blois comes over to her side, and Winchester opens the treasury to her. But she fails to win over London, and generally alienates everyone she can find. London rises up in fury, and throws her out. She is forced to flee without even having time to finish supper.
The Rout of Winchester
Henry of Blois again transfers his allegiance, back to Stephen, and besieges the Empress's castle at Winchester. And when the Empress comes down with her army to get it back, Queen Matilda and William of Ypres bring Stephen's army down and trap the Empress. Things get desperate. The Empress breaks out, but Robert of Gloucester is not so lucky, and is captured. So at the end of 1141, Stephen is released from captivity in exchange for Robert, and the game is back on.