Saoirse Ronan is the latest addition to the cast of Ryan Gosling’s helming debut “How to Catch a Monster.” The Irish actress joins “Doctor Who” star Matt Smith, Eva Mendes and Ben Mendelsohn in the roster of recently added talent on the project.The modern fantasy drama, which is also scripted by Gosling, stars his “Drive” co-star Christina Hendricks and is set to lense in Detroit in May. Hendricks stars as a single mother who is swept into a macabre and dark underworld while her teenage son discovers a secret road leading to an underwater town. The pair must delve deeper into the mystery in order for their family to survive. Marc Platt and Adam Siegel will produce for Marc Platt Productions alongside Bold Films’ Michel Litvak and David Lancaster, and Gosling via his Phantasma Films banner. Ronan was Academy Award nominated for her role in Joe Wright’s 2007 film “Atonement” and will next be seen heading the cast of Stephenie Meyer adaptation “The Host” which opens in March. Sierra/Affinity is handling international sales at the EFM.