Morris is never actually present in the novel but he is hired by Wargrave to purchase the island under the name of Mr. Owen, and find plausible ways to invite all the guests. Owen is a shady businessman who has been involved in the drug trade and convinced a daughter of one of Wargrave's friends to start taking drugs, after which she committed suicide. Wargrave is able to kill Morris with poison even though Morris never comes to Soldier Island, and Morris leaves no trace of Wargrave's presence in the business dealings that enabled the multiple murders on Soldier Island.
The timeline below shows where the character Isaac Morris appears in And Then There Were None. The colored dots and icons indicate which themes are associated with that appearance.