There is no duty to retreat into one's home or place of work under Michigan law. The use of deadly force in defense of one's self or others is justified if the person believes the aggressor with kill them or severely injure them.
Castle Laws are laws that address the use of force when defending one's self inside their home, or on their property. Some states expand this to vehicles, and the person's place of work. Castle Laws generally include: the places where this law applies, the requirements fro use of deadly force, if there is a duty to retreat, the amount of force that maybe used in defending one's self or others. These vary widely from state to state.