It gets better. "God's Plan" and free will are incompatible, yes. But also, Christians love to pray for stuff. "Make mama get better", "Let the Cowboys win", "Get me the job I want", etc. And they LOVE to say that "prayer works". But at no point do they consider the implications of that notion, that praying for things changes the outcomes of the world.
A) Anything, prayer or otherwise, that can change the trajectory of events is, like free will, wholly incompatible with the notion that the universe is following in lockstep with "God's Plan".
B) If absolutely anything would be part of God's Plan, according the Christian faith, it would be the birth and death of every human. This is directly incompatible with prayer saving someone's life.
C) Changing the outcome of any choice a person is going to make (such as hiring decisions), is also wholly incompatible with free will.
D) The very notion of prayer causing change places human agency over God's will. Yes, presumably, God could choose whether for not to grant a prayer. However, if he changes his prescribed outcomes based on your prayer, then that means either that he decided your idea was better (which seems odd for an all-knowing being) or decided to capitulate to you for some reason. Either way, you hold sway over your almighty god's will for the universe. This thought is SUUUPER narcissistic to believe in.
E) Other people's prayer holds sway over you. If your prayer can cause God to change the minds of others, then their prayers can likewise cause God to change your mind in turn. Neither of you then has free will. Moreover, it is not just God, ultimately, that can negate your free will, but any other Christian that prays for it. That's troubling, to say the least.
F) Bad things, things unjustified by karmic justice, things unrelated to human free will, happen all the time. Things like natural disasters, disease, animal attacks, genetic accidents, etc. Those things happen to good people, Godly people, innocents, infants, the unborn. People pray for these things not to happen. "God, Protect them", "Bless them with your Grace", "Watch over them". Yet they still happen. If prayers works, unless God decides to not answer them, then God must have decided to ignore those prayers. Prayer working is, itself, incompatible with the idea that there is a holy plan that must be followed, so that is not a justification for choosing to ignore those prayers and allow such things to happen. That means God could have stopped it and did not. God is directly responsible for these evils. There is no way around that.
On that happy note, enjoy your Sunday service guys!