They're able to locate Arthur, but he's a bit of a scoundrel himself and assumes the two have more nefarious reasons for tailing him.
This was the final feature film of Hitchcock's career, and it is an interesting last project, as Family Plot is a dark comedy with hints of suspense thrown in for good measure. An elderly woman hires Blanche (Barbara Harris), a slightly shady psychic, and George (Bruce Dern), Blanche's very shady boyfriend, to track down Arthur (William Devane), her long lost nephew. They're able to locate Arthur, but he's a bit of a scoundrel himself and assumes the two have more nefarious reasons for tailing him. It's not an all-timer, but Family Plot is a fun, seedy romp that shows off Hitchcock's genre range.