The tale of Zipporah at the inn, is one of the more unusual, curious, and much-debated, passages of the Torah.
When Moses and Zipporah reach an inn:
On the way, at a place where they spent the night, the LORD met him and tried to kill him. But Zipporah took a flint and cut off her son's foreskin, and touched his [?Moses'] feet with it, and said, "Truly you are a bridegroom of blood to me!" So he let him alone. It was then she said, "A bridegroom of blood by circumcision."
Exodus 4:24–26 (NRSV, with pronoun reinstated)
While the passage is frequently interpreted as referring to Gershom, Moses' firstborn, being circumcised, the Midrash actually states that the passage was, at that time, considered instead to refer to Eliezer, Moses' other son.
Given the abrupt change in many of these interpretations, several critical scholars have suggested that this passage, usually considered under the documentary hypothesis to belong to the Jahwist, may have originally contained additional verses, toward the beginning of the tale, which have since become excised for an unknown reason. Such verses would be expected to explain the reason for God's anger.
The Septuagint version is subtly different
"Angel" (gr.,"angelos") is the translation throughout the Septuagint of the Hebrew "mal'ak", the term for the manifestation of God to humanity. (It is the mal'ak that speaks to Moses from the burning bush). So it is implied in this passage that it is God (God) himself who attempts to kill Moses.
The version in the Book of Jubilees (usually considered non-canonical, but nevertheless dating from the second century BC and presented as a direct revelation "to" Moses from an Angel) is yet different still. It absolves God by attributing the attempted murder to Prince Mastema, a title that was another name for Satan:
... and what Prince Mastema desired to do with you when you returned to Egypt, on the way when you met him at the shelter. Did he not desire to kill you with all of his might and save the Egyptians from your hand because he saw that you were sent to execute judgment and vengeance upon the Egyptians? And I delivered you from his hand and you did the signs and wonders which you were sent to perform in Egypt. - Jubilees 48:2-4