The Healer by Berkley and the Tery by Baen overlap the with the original story "Pard" however The Healer takes a longer time view than The Tery and hence feels more complete with its historical references and multiple time lined stories which jump forward in time 50, 200, 500 years. If you read only one story by Wilson Read The Tery, if you want more then follow up with the Healer, this helps explains what happens next. I enjoyed the unique story line, engendered by "Pard" an alien Symbiote with benefits, I wondered if Star Gate Authors had read Pard, before designing their story? Good Solid Sci-fi a Classic. How would you feel with a friendly Alien in you? The Star gate people took this question to the negative aspect.