There is a famine and Isaac moves around a bit. They end up back in Philistine and Isaac tells everyone Rebekah is his sister. But the king (Abimelech) sees Isaac and Rebekah together and wants to know why he lied. Same old story – didn’t want to be killed just because his wife is beautiful. He is allowed to stay and he becomes very wealthy. The Philistines grow jealous and tell him to leave. He does and every well he digs to find water, the philistines contest. He finally gets a well no one challenges him over and thinks all is well. But the king Abimelech comes and wants to create a covenant of peace. Esau gets married to a Hittite and this upsets Isaac and Rebekah.
In other words:
Once Abraham dies, the Philistines start to reclaim his wells and land. There is a famine which is probably driving this. Eventually Isaac cuts the same deal with the king as his father did and all is well once again, except that their oldest son Esau married a (gasp) Hittite.
That marrying a Hittite is cause for grief (Genesis 26:35)
Moral Lesson Learned:
If at first you don’t succeed, try try again (Genesis 26:18-22)