The Fosters 4×17 “Diamond In The Rough” Season 4 Episode 17 Sneak Peek – Stef aims to save a girl from a life of violence and prostitution, on an all-new episode of “The Fosters,” airing Tuesday, March 21st, on Freeform. Stef starts a new assignment in human trafficking where she meets a teenaged girl named Diamond who is turning tricks on the streets. Lena deals with repercussions for holding an off-campus LGBTQ sex ed class for Anchor Beach students. Callie’s relentless pursuit of justice starts to impact her relationship with AJ. Meanwhile, Mariana tries to cheer up Jesus with a special project after he’s prescribed a special pair of glasses due to his traumatic brain injury.