Overview
Gwent: Old Pals is a secondary quest in The Witcher 3: Wild Hunt, played in and around Novigrad and at Kaer Morhen. It is required for the Card Collector achievement, and it starts when Geralt beats Zoltan at gwent.
Zoltan
Zoltan only plays at certain moments. During Broken Flowers you can play him after reporting back on the girls, or as he leaves at the end. Otherwise you have to wait until after A Poet Under Pressure. He gives the Eithné card and sends you to Roche.
Roche
Vernon Roche is at the Temerian partisan hideout. He gives the Saesenthessis card and points to Lambert, and to Thaler if A Deadly Plot is already done.
Lambert
The easiest chance to play Lambert comes during Following the Thread, at the Seven Cats Inn or later at The Nowhere Inn. If you miss him, he can be challenged at Kaer Morhen. A game during No Place Like Home also counts, and if he survives the battle you get one last chance at the funeral in Blood on the Battlefield. He gives the Triss Merigold card.
Thaler
If A Deadly Plot was finished before you played Roche, Thaler joins the chain. He sits at the Seven Cats Inn and gives the powerful Geralt of Rivia card. He cannot be played during Reason of State and can die there, so play him first. Otherwise he gets his own quest, Gwent: Playing Thaler.
If one of them dies before you play him, the quest adds objectives to find his card instead, so it can still be completed.
