Genesis 20 – Skeptic's Annotated Bible answered

1 And Abraham journeyed from thence toward the south country, and dwelled between Kadesh and Shur, and sojourned in Gerar.

2 And Abraham said of Sarah his wife, She is my sister: and Abimelech king of Gerar sent, and took Sarah.

(20:2) "Abraham said of Sarah his wife, She is my sister."
Honest Abe does the same "she's my sister" routine again, for the same cowardly reason. And once again, the king just couldn't resist Sarah -- even though by now she is over 90 years old. (See Genesis 12:13-20 for the first, nearly identical, episode, and 26:7 for another repeat with Isaac, Rebekah and the same king Abimelech.)
Theocratic War Strategy

3 But God came to Abimelech in a dream by night, and said to him, Behold, thou art but a dead man, for the woman which thou hast taken; for she is a man’s wife.

4 But Abimelech had not come near her: and he said, Lord, wilt thou slay also a righteous nation?

5 Said he not unto me, She is my sister? and she, even she herself said, He is my brother: in the integrity of my heart and innocency of my hands have I done this.

6 And God said unto him in a dream, Yea, I know that thou didst this in the integrity of thy heart; for I also withheld thee from sinning against me: therefore suffered I thee not to touch her.

7 Now therefore restore the man his wife; for he is a prophet, and he shall pray for thee, and thou shalt live: and if thou restore her not, know thou that thou shalt surely die, thou, and all that are thine.

8 Therefore Abimelech rose early in the morning, and called all his servants, and told all these things in their ears: and the men were sore afraid.

9 Then Abimelech called Abraham, and said unto him, What hast thou done unto us? and what have I offended thee, that thou hast brought on me and on my kingdom a great sin? thou hast done deeds unto me that ought not to be done.

10 And Abimelech said unto Abraham, What sawest thou, that thou hast done this thing?

11 And Abraham said, Because I thought, Surely the fear of God is not in this place; and they will slay me for my wife’s sake.

12 And yet indeed she is my sister; she is the daughter of my father, but not the daughter of my mother; and she became my wife.

13 And it came to pass, when God caused me to wander from my father’s house, that I said unto her, This is thy kindness which thou shalt shew unto me; at every place whither we shall come, say of me, He is my brother.

14 And Abimelech took sheep, and oxen, and menservants, and womenservants, and gave them unto Abraham, and restored him Sarah his wife.

15 And Abimelech said, Behold, my land is before thee: dwell where it pleaseth thee.

16 And unto Sarah he said, Behold, I have given thy brother a thousand pieces of silver: behold, he is to thee a covering of the eyes, unto all that are with thee, and with all other: thus she was reproved.

17 So Abraham prayed unto God: and God healed Abimelech, and his wife, and his maidservants; and they bare children.

18 For the LORD had fast closed up all the wombs of the house of Abimelech, because of Sarah Abraham’s wife.