Linden was doubled over against the wall, his read resting on the cold stone. Clearly in some major discomfort, and in the dark, the guard didn't see the bandit crawling towards him. Without a light stone, or a torch, it was virtually impossible to see anything in the cave.
--
From his vantage point on the other side of the tunnel entrance, Mavis was looking into and towards what little light there was offered by the tunnel on the far side. Due to this, he was able to see the silhouettes of most of the people in the tunnel, including the bandit who was slinking towards Linden. Expecting the guard to hear the bandit, Mavis initially stayed put. He had every bit of faith in Linden's ability to kick butt. When his friend didn't move, however, Mavis became alarmed that maybe Linden did not hear the bandit, and was not going to move.
He tightened his grip around the sword, partially to make sure it was still there and that he wasn't dreaming. When the handle of the sword felt firm in his grasp, he started to make his way slowly and cautiously across the mouth of the tunnel. His footsteps were small and quiet, which was partially a counter-measure, and also because his battered body simply couldn't manage anything faster. In about six or seven feet, the bandit would either kill Linden and Mavis... or Mavis was going to do something about it.