Inclusion Criteria :

          1. Patients must be at least 18 years of age on the day of signing informed consent.

          2. Patients must have first or second peritoneal recurrence of epithelial adenocarcinoma
             or carcinosarcoma of ovarian, tubal or peritoneal origin:

               1. Histologic documentation of the original primary tumor is required via the
                  pathology report.

               2. Original tumor blocks from the primary diagnosis will be requested by our study
                  pathologist at Magee-Women's Hospital of UPMC Cancer Centers if the patient did
                  not have their initial surgery at Magee. Original tumor blocks may be reviewed
                  after registration (informed consent and enrollment). Tumor block should be held
                  until study is completed.

          3. Patients must have completed prior platinum-based therapy. Response can be complete or
             partial if it otherwise meets platinum sensitive criteria, see below.

          4. Patients must be platinum-sensitive, defined as having a progression free interval
             (PFI) of more than 6 months (180 days) from any platinum therapy. Patients are allowed
             to have had other lines of therapy since last platinum if PFI after platinum therapy
             meets platinum sensitive criteria.

          5. Patients must have measurable disease in the peritoneal cavity, measurable per RECIST
             1.1 criteria:

               1. A mass with a length of 1.0 cm or greater and/or

               2. A lymph node with a length of 1.5 cm or greater in the shortest axis.

          6. Patients must be a reasonable candidate for laparoscopy and IP platinum regimen with
             no prior evidence of clinically significant intra-abdominal adhesions, persistent
             abdominal wall infections, renal toxicity or bowel obstruction.

          7. Patients of childbearing potential must:

               1. Have a negative pregnancy test prior to the study entry.

               2. Must discontinue breastfeeding prior to the first date of treatment on this study
                  if applicable.

               3. Agree to follow the contraceptive guidance in Appendix 3 during the treatment
                  period and for at least 120 days after the last dose of study treatment.

          8. Patients must agree to the protocol designated clinical monitoring to receive the
             study regimens.

          9. The participant provides written informed consent for the trial.

         10. Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1.
             Evaluation of ECOG is to be performed within 28 days prior to the date of
             allocation/randomization.

         11. Have adequate organ function as defined in the following table (Table 1). Specimens
             must be collected within 28days prior to the start of study treatment.

        Exclusion Criteria :

          1. A WOCBP who has a positive urine pregnancy test within 72 hours prior to infusion of
             treatment regimen (see Appendix 3). If the urine test is positive or cannot be
             confirmed as negative, a serum pregnancy test will be required. Note: in the event
             that 72 hours have elapsed between the screening pregnancy test and the first dose of
             study treatment, another pregnancy test (urine or serum) must be performed and must be
             negative in order for subject to start receiving study medication

          2. Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti PD L2 agent or with
             an agent directed to another stimulatory or co-inhibitory T-cell receptor (e.g.,
             CTLA-4, OX 40, CD137).

          3. Has received prior systemic anti-cancer therapy including investigational agents
             within 4 weeks prior to allocation.

               -  Note: Participants must have recovered from all AEs due to previous therapies to
                  ≤Grade 1 or baseline. Participants with ≤Grade 2 neuropathy may be eligible.

               -  Note: If participant received major surgery, they must have recovered adequately
                  from the toxicity and/or complications from the intervention prior to starting
                  study treatment.

          4. Has received prior radiotherapy within 2 weeks of start of study treatment.
             Participants must have recovered from all radiation-related toxicities, not require
             corticosteroids, and not have had radiation pneumonitis. A 1-week washout is permitted
             for palliative radiation (≤2 weeks of radiotherapy) to non-CNS disease.

          5. Patients with previous pelvic radiation therapy.

          6. Has received a live vaccine within 30 days prior to the first dose of study drug.
             Examples of live vaccines include, but are not limited to, the following: measles,
             mumps, rubella, varicella/zoster (chicken pox), yellow fever, rabies, Bacillus
             Calmette-Guérin (BCG), and typhoid vaccine. Seasonal influenza vaccines for injection
             are generally killed virus vaccines and are allowed; however, intranasal influenza
             vaccines (e.g., FluMist®) are live attenuated vaccines and are not allowed.

          7. Is currently participating in or has participated in a study of an investigational
             agent or has used an investigational device within 4 weeks prior to the first dose of
             study treatment.

             o Note: Participants who have entered the follow-up phase of an investigational study
             may participate as long as it has been 4 weeks after the last dose of the previous
             investigational agent.

          8. Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy
             (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of
             immunosuppressive therapy within 7 days prior to the first dose of study drug.

          9. Patients with tumors of low malignant potential, except ovarian pseudomyxomas, or with
             no peritoneal disease.

         10. Concurrent malignancy or malignancy within 3 years prior to starting study drug, with
             the exception of adequately treated basal or squamous cell carcinoma, non-
             melanomatous skin cancer or curatively resected cervical cancer or per physician
             discretion that the previous cancer was adequately treated with curative intent and
             unlikely to recur (the study PI must concur with this determination).

         11. Has known active CNS metastases and/or carcinomatous meningitis. Participants with
             previously treated brain metastases may participate provided they are radiologically
             stable, i.e. without evidence of progression for at least 4 weeks by repeat imaging
             (note that the repeat imaging should be performed during study screening), clinically
             stable and without requirement of steroid treatment for at least 14 days prior to
             first dose of study treatment.

         12. Has severe hypersensitivity (≥Grade 3) to pembrolizumab and/or any of its excipients.

         13. Has a known allergy to cisplatin chemotherapy. Patients with carboplatin allergy may
             be included if they tolerate a test dose of IV cisplatin given in monitored floor
             conditions.

         14. Has active autoimmune disease that has required systemic treatment in the past 2 years
             (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive
             drugs). Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid
             replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a
             form of systemic treatment.

         15. Has a history of (non-infectious) pneumonitis that required steroids or has current
             pneumonitis.

         16. Has an active infection requiring systemic therapy.

         17. Has a known history of Human Immunodeficiency Virus (HIV). Note: No HIV testing is
             required unless mandated by local health authority.

         18. Has a known history of Hepatitis B (defined as Hepatitis B surface antigen [HBsAg]
             reactive) or known active Hepatitis C virus (defined as HCV RNA qualitative is
             detected) infection. Note: no testing for Hepatitis B and Hepatitis C is required
             unless mandated by local health authority.

         19. Has a known history of active TB (Bacillus Tuberculosis)

         20. Has a history or current evidence of any condition, therapy, or laboratory abnormality
             that might confound the results of the study, interfere with the subject's
             participation for the full duration of the study, or is not in the best interest of
             the subject to participate, in the opinion of the treating investigator.

         21. Has known psychiatric or substance abuse disorders that would interfere with
             cooperation with the requirements of the trial.

         22. Is pregnant or breastfeeding, or expecting to conceive or within the projected
             duration of the study, starting with the screening visit through 120 days after the
             last dose of trial treatment.