Inclusion Criteria:

          -  Patients must be ≥ 18 years of age

          -  Histologically diagnosed relapsed high grade epithelial ovarian cancer (including
             primary peritoneal and/ or fallopian tube cancer)

          -  Documented deleterious or suspected deleterious somatic BRCA 1 and/or BRCA 2 somatic
             mutation or evidence of non- BRCA HRR-associated gene mutation in the tumour.

          -  At least 2 previous lines of platinum containing therapy prior to randomisation.

          -  CA-125 measurements prior to randomised treatment

          -  Patients must have normal organ and bone marrow function measured within 28 days of
             randomisation

          -  Eastern Cooperative Oncology Group (ECOG) performance status 0-1

          -  Postmenopausal or evidence of non-childbearing status for women of childbearing
             potential

          -  Patient is willing and able to comply with the protocol for the duration of the study
             including undergoing treatment and scheduled visits and examinations

          -  Provision of a blood sample for cfDNA biomarker analysis in Pre-Screening Part 1

          -  Formalin fixed, paraffin embedded (FFPE) tumour sample from the primary or recurrent
             cancer must be available for central testing. If archival tumour sample is not
             available tumour sample from fresh biopsy is acceptable, for all patients eligible to
             participate in Pre-Screening part 2.

        Exclusion Criteria:

          -  Documented germline mutation in BRCA1 and/or BRCA2 that is predicted to be deleterious
             or suspected deleterious (known or predicted to be detrimental/lead to loss of
             function).

          -  Patients who have had drainage of their ascites from the final 2 cycles of their last
             chemotherapy regimen prior to randomisation on the study

          -  Participation in another clinical study with an investigational product during the
             chemotherapy course immediately prior to randomisation

          -  Any previous treatment with a PARP inhibitor, including olaparib

          -  Patients with a known hypersensitivity to olaparib or any of the excipients of the
             product

          -  Prior malignancy in the last 5 years, unless curatively treated and recurrence free
             (few exceptions apply)

          -  Patients receiving any systemic chemotherapy (including chemotherapy received as the
             most recent anticancer therapy) or radiotherapy (except for palliative reasons) within
             3 weeks prior to study randomised treatment

          -  Persistent toxicities (>Common Terminology Criteria for Adverse Event (CTCAE) CTCAE
             grade 2) caused by previous cancer therapy, excluding CTCAE grade 2 peripheral
             neuropathy

          -  Patients with myelodysplastic syndrome/acute myeloid leukaemia (t-AML) or with
             features suggestive of MDS/AML

          -  Patients with symptomatic uncontrolled brain metastases

          -  Major surgery within 2 weeks of starting study randomised treatment and patients must
             have recovered from any effects of any major surgery

          -  Patients considered a poor medical risk