I forgot to include the following sentences which belong to the same summary. Thank you.
1) While building up the personality of Kurtz for his listeners, Marlow exposes the discrepancy between the Europeans’ words and their actions.
2) At the beginning Kurtz is presented as an idealist. Then, he is described as a ruthless exploiter, who is prepared to kill for a little ivory. Instead of turning his station into a centre for improving the colonized, he has given in to his desires.
3) He has decorated the poles around his house with human skulls and has participated in unspeakable rites.
4)The postscript to his report “kill all the brutes” reveals the failure of white civilization to put its ideals into practice.
5) " A calendar hangs to (Could you say ON?) the right of the door.
#1 comma following listeners, not a semi-colon.
#4 "on" would be correct.