With the number of Scotland's prisoners approaching a record high, Lucy Adams investigates the impact of overcrowding, drugs and suicides on inmates and staff, and asks whether the crumbling prison estate can cope much longer. She meets families grieving the loss of their loved ones on the inside and sheds new light on one of Scotland's most high-profile deaths in custody. She also goes inside one of the country's largest prisons to witness first-hand a system on the brink