Mallard went on to play the recurring role of Lucas Caravaggio in the Netflix horror series Locke & Key: a 17-year old friend of Rendell Locke, who died 25 years earlier, after being possessed by a demon. Filming took place in the first half of 2019. It was released on 7 February 2020. He appeared in the romantic drama film All the Bright Places, which began filming in October 2018 and was also released by Netflix in February 2020. The film is an adaptation of Jennifer Niven's 2015 young adult novel of the same name.
