In the first story about Abram after his calling, he goes down to Egypt because of a famine and Pharaoh takes Abram's wife Sarai into his household. As a result God inflicts Pharaoh with plagues.

But the Lord inflicted serious diseases on Pharaoh and his household because of Abram’s wife Sarai. So Pharaoh summoned Abram. "What have you done to me?" he said. "Why didn’t you tell me she was your wife?"

I realize the text is thin here, but how does Pharaoh know to summon Abram? Later in Genesis 20 when a similar even happens with Abimelek, God speaks to Abimelek in a dream to tell him he is a dead man. Abimelek protests he has a clean conscience. But nothing like that happens here. Should we infer in the Genesis 12 story that Pharaoh knew Sarai was Abram's wife, even if there was a charade among all parties to pretend otherwise?