Season 4 of HBO's hit comedy opens on location in Colombia with a documentary-style look at the making of "Medellin," the long-awaited dream project of Vincent Chase (Adrian Grenier) about drug lord Pablo Escobar. On set, erratic director Billy Walsh (Rhys Coiro) reveals the film doesn't have an ending, so first-time producer Eric Murphy (Kevin Connolly) hires Oscar-winning writer Stephen Gaghan (playing himself) to finish the script, only to have Billy eventually do it himself. Upon returning to L.A., Vince is short on cash since financing "Medellin," so the boys stay with Johnny Drama (Kevin Dillon) in his newly acquired condo. After years of failure, Drama finally gets a taste of success with a starring role in the hit (but critically panned) TV drama "Five Towns." Vince learns from agent Ari Gold (Jeremy Piven) that the future of his once red-hot career is now riding on the success of "Medellin" and no studios are willing to sign him until they see the film, prompting Eric and Vince to have Walsh speed up its release. When Walsh does finally show them the final cut, Vince is pleased while Eric is less than impressed. And to make matters worse, Walsh sends it to the Cannes Film Festival before incorporating any of their feedback. Fed up with Walsh, Eric tries to ditch him by offering to sell "Medellin" to Hollywood heavyweight Harvey Weingard (Maury Chaykin), but when the film's trailer is leaked online and the reception is positive, Eric realizes he may have made a mistake. The entire experience encourages Eric to stop riding Vince's coattails, so he branches out and takes on Anna Faris (playing herself) as a new client, even though her jealous boyfriend is none too happy with the arrangement. As usual, this season is chock-full of celebrity guest stars, including Dennis Hopper, Anthony Michael Hall, Snoop Dogg, Gary Busey, Mary J. Blige, Peter Jackson, Kanye West and Sydney Pollack.