Caterpillar right inside hot rock (5)
I believe the answer is:
larva
'caterpillar' is the definition.
(I've seen this in another clue)
'right inside hot rock' is the wordplay.
'right' becomes 'r' (common abbreviation).
'inside' is an insertion indicator.
'hot rock' becomes 'lava' (I've seen this in another clue).
'r' put into 'lava' is 'LARVA'.
(Other definitions for larva that I've seen before include "Early stage of creature" , "early form" , "a developmental stage" , "Grub, caterpillar stage" , "Manage" .)