Mike was really going back to Valtrar while Jack willed to stay behind. However, he ended up coming back to where he left them. It took a while to reach that place since it was far from Valtrar and yet still in human territory, but in Plaguelands.
There was one thing Stephan needed to keep a secret: the fact that he was Maddock Prowell. It would be bad for him and right now, he didn't wish to kill Jack. They found a place near a river and at the same time with no thick miasma. They needed to get the fire working and light everywhere for the Night Grim to not come.
In fact, Stephan didn't care for that monster since he understood from his diary, because it was his diary, that as long as he had a part of Aurora, he would be fine. However, he didn't want Jack to learn about it, so he needed to put on a display of fear.