Heisserer's professional screenwriting career was launched with the sale of The Dionaea House to Warner Bros. in 2005, based on an online epistolary story of the same name that he wrote in October 2004. He then developed an original television pilot for Paramount Pictures and CBS, and wrote feature projects for Jerry Bruckheimer Films and Warner Bros.. In 2007, he sold a pitch to Regency Enterprises and Fox called Inhuman, a supernatural thriller set in Tokyo that combines live action and anime sequences.