The use of robots in wireless sensor networks (WSNs) opens up opportunities for new applications such as search and rescue in harsh environments. In WSNs, since GPS is not usually used due to the limited power of sensors, the nodes do not know their positions. In this paper, we tackle the problem of locating a sensor node in a field of randomly deployed sensors. Neither the mobile node (the robot) nor the sensors have any prior knowledge about their locations. When a sensor (the source node) detects a dangerous event in the environment, it broadcasts a message to the entire network to ask for the mobile robot's help.