I have bits and pieces of this in my head. For some reason, the protagonist is being pursued by hired killers. I want to say that he knows that they're coming from the beginning. They're all themed, all famous, with the chapters being introduced with bits of verse like nursery rhymes describing their usual tactics, but only one of them is sticking in my head. One of the assassins is known as "Simple Simon" with the rhyme riffing off of the traditional nursery rhyme with him killing the pieman for his pies. Either that assassin or one close in time to him attempts to kill the protagonist by rigging their showerhead (might have been a sonic shower) with lasers, and is killed by being forced into it.
Other than that, my mind is blank. It was a paperback. I read it somewhere in the 1990s in the United States in English.