This randomized, double blind, phase II study will evaluate the efficacy and safety of two doses of RO5024048 in combination with ritonavir-boosted danoprevir and Pegasys (peginterferon alpha-2a) and Copegus (ribavirin) in patients who failed a prior protease inhibitor containing regimen with or without pegylated interferon. Patients will be randomized to receive either a 2-week lead-in of RO5024048 (1500 mg or 1000 mg orally twice daily) in combination with Pegasys (180 mcg subcutaneously weekly) and Copegus (1000 mg or 1200 mg orally daily) followed by 24 weeks of therapy with RO5024048 in combination with danoprevir (100 mg orally twice daily) plus ritonavir (100 mg orally twice daily) and Pegasys and Copegus (QUAD therapy), or 24 weeks of therapy with RO5024048 in combination with danoprevir plus ritonavir and Pegasys and Copegus (QUAD therapy). Anticipated time on study treatment is 24 or 26 weeks, with a treatment-free follow-up of 24 weeks.