The side quest starts with Siegmeyer of Catarina sitting on the steps of Sen's Fortress. The full quest line also include his daughter, Sieglinde of Catarina. There are number of different possible outcomes, all depend on meeting certain conditions.
- Speak to Siegmeyer of Catarina outside Sen's Fortress, when the gate is closed.
- After opening the gate, enter Sen's Fortress and head down the outside boulder track to locate and speak to Siegmeyer again. It is possible that this step is optional.
- Locate Siegmeyer in upper area of Anor Londo, defeat a bunch of Knights, talk again and Siegmeyer will give you Tiny Being's Ring.
- With the Lordvessel, warp to Firelink Shrine and have a chat. Siegmeyer will give you Emit Force if you answer yes.
- In Blighttown, head towards The Great Hollow / Giant Leech area, locate Siegmeyer and give him a Purple Moss Clump (3x). Gives you Pierce Shield.
- Heading out of the The Duke's Archives towards the Crystal Cave, is a Golden Crystal Golem, defeat it and out pops Sieglinde of Catarina. Answer yes to any question.
- Back to Firelink Shrine, talk with Sieglinde again, answer yes to any question.
- Now it gets complex. Locate Siegmeyer in Lost Izalith, below the final fog gate. Kill almost all of the Chaos Eaters before you talk to Siegmeyer. Talk to him, help him fight but let him hit something. Talk after the fight.
- At Firelink Shrine, chat with Sieglinde, answer yes to questions. You may have to talk more than once. After She talks about a Final Mission, head to Ash Lake.
- By the first Bonfire at Ash Lake, you can find them. Sieglinde will give you a Titanite Slab.
Siegmeyer of Catarina outside Sen's Fortress. Your first meeting with this Knight and the start of the Catarina side quest.
Kill Sieglinde at any time, drops 1,000 Souls only.
Siegmeyer does not survive against the Chaos Eaters, or you defeat all of them, drops or gives Speckled Stoneplate Ring.