"A Slitheen is something you don't want to mess with on a bad day," The Doctor told Leander, leading him away from the crater of water. "They're viscous hunters who can smell age, adrenaline and mainly fear. Thankfully, this thing-" the Doctor held up the tracking object. "-is dead. Must have been here a couple of days, so the Slitheen shouldn't have strayed to far from home." 

The Doctor let go of Leander's arm and surveyed his surrounds. Masses of countryside surrounded the area, mountains of green swept for miles. The Slitheen could be anywhere. 

"Tell me Leander, has there been any disappearances or any strange goings on in the past week? Anything brutal?" The Time Lord asked the young boy as they continued to walk over a desolated field.