He wrote the story with his friend's 'assistance'. = He wrote the story 'with the assistance of' his friend. [=his friend helped him to write the story]
Our family had to 'go on public assistance' [=receive money from the government] when my parents lost their jobs.
Nobody 'came to her assistance' [=nobody helped her] when her car broke down.
(..) No. No, I crack this code, all the smugglers have to do is pick up another book. SIREN BLARES Without you... without your assistance, we would not have found passage into London. You have my thanks. We did not anticipate... We did not know this man would come. (..)2010 TvShow: Sherlock Title: The Blind Banker Season: 1 Episode 2