SPOILER ALERT!! - Abby (Julie Graham) learns of a group of young boys living at a nearby mansion called Waterhouse. She is determined to see if Peter is there, and leaves her new friends in order to find her son. When she arrives at Waterhouse, she walks into the middle of a land dispute between Jimmy Garland (Joseph Millson), an ex-Army officer who has an ancestral claim to the mansion, and an aggressive group of teenage boys who have taken up residence there.
In Abby's absence, her surrogate family is in danger of falling apart. Tom (Max Beesley), Sarah (Robyn Addison), Al (Philip Rhys) and Najid (Chahak Patel) are drawn to the comfort and security that Samantha's (Nikki Amuka-Bird) community provides. Tom settles into his new surroundings quickly and starts to see himself in a position of power in the new society that Samantha hopes to build.
Things quickly go wrong for Al, however, as he is ejected from the community when Samantha decides he will not fit in. Tom sees the chance to prove himself to Samantha, but will his criminal past catch up with him? Meanwhile, Greg (Patterson Joseph) and Anya (Zoe Tapper) are left to protect the survivors' house alone, and an encounter with some unwelcome visitors provides a vivid reminder of how vulnerable they are without the group. Episode four airs Saturday, March 6th @ 9:00 p.m. EST on BBC America.