The tribe of Ephraim is annoyed that Jephthah didn't include him in the slaughter of the Ammonites, and threatens to burn his house down. Well, that's convincing! Jephthah answers that he did call for them, but they didn't help, so he asked for, and received, assistance from god.
These taunts and insults lead to a war. The Gileadites take control of a bridge over the river Jordan and set up a checkpoint. Anyone wanting to cross is asked to say the word 'Shibboleth', but the Ephraimites can't say the 'sh' sound, so they say 'Sibboleth,' which is how we got that word. Anyone who mispronounces it is put to death. 42 000 Ephraimites die that way. I guess Hooked on Phonics didn't work for them. The Dutch famously used this technique in WWII as a way of finding out German spies. They used the word 'Scheveningen' as a password, because it's hard for non-Dutch speakers to say correctly.
Jephthah dies after 6 years, and then a series of unremarkable Judges rules. We hear a lot about how many sons they had, and how many asses, but nothing in the way of real accomplishments. But never fear, Samson is up tomorrow to render this book exciting again!