Heard two characters in shelter (6)
I believe the answer is:
teepee
'shelter' is the definition.
(I know that teepee is a type of tent)
'heard two characters' is the wordplay.
'heard' shows a homophone (sound like).
'two characters' becomes 'TP'.
'tp' sounds like 'TEEPEE'.
'in' acts as a link.
(Other definitions for teepee that I've seen before include "Wigwam" , "Conical American Indian tent" , "Cone-shaped tent of animal skins" , "Tent used by American aborigines" , "N. American native tent" .)