: Max (Jessica Alba) and Logan (Michael Weatherly) search for Joshua, the canine-enhanced transgenic who helped Max escape. They discover Joshua is on his own hunt to find his "father" or creator, Sandeman.
In this episode, the narrative follows three major threads that deepen the show's post-apocalyptic lore:
: Alec (played by Jensen Ackles) is coerced by Ames White into a hunt for other Manticore escapees. White plants a small, remote-detonated bomb at the base of Alec's skull, demanding the barcodes of three transgenics as "proof of purchase" for his life.
"Proof of Purchase" is noted by reviewers for advancing the "Sandeman mystery" and establishing the complex, often adversarial chemistry between Max and Alec. Although the show was canceled after its second season, this episode remains a fan favorite for its high stakes and character development. "Dark Angel" Proof of Purchase (TV Episode 2001) - IMDb