Inclusion Criteria:

          -  Subjects must have histologically confirmed diagnosis of multiple myeloma

          -  Subjects must have measurable disease, as defined by at least one of the following:

               -  Serum monoclonal protein M-protein level >= 0.5 g/dL

               -  Urinary M-protein excretion of >= 200 mg over a 24-hour period

               -  Involved free light chain level >= 10 mg/dL, along with an abnormal free light
                  chain ratio

          -  Subjects must have disease that has relapsed and/or refractory after their most recent
             therapy, with progressive disease (PD) being defined as an increase of 25% from the
             lowest response value in any one or more of the following:

               -  Serum M-component protein (the absolute increase must be >= 0.5 g/dL) and/or

               -  Urine M-component protein (the absolute increase must be >= 200 mg/24 hours)
                  and/or

               -  Only in subjects without a measurable serum and urine M protein level: the
                  difference between involved and uninvolved free light chain (FLC) levels
                  (absolute increase) must be > 10 mg/dL

               -  Definite development of new bone lesions or soft tissue plasmacytomas or definite
                  increase in the size of existing bone lesions or soft tissue plasmacytomas

               -  Development of hypercalcemia (corrected serum calcium > 11.5 mg/dL) that can be
                  attributed solely to the plasma cell proliferative disorder

          -  Subjects with one to three lines of therapy for their disease with a line of therapy
             defined as one or more cycles of a planned treatment program; using this definition,
             treatment with induction therapy, followed by high dose chemotherapy and autologous
             stem cell transplantation, and finally by maintenance therapy, would constitute one
             line, provided that multiple myeloma did not meet criteria for progression at any time
             during this period

          -  Subjects must have completed their most recent drug therapy directed at multiple
             myeloma in the following timeframes:

               -  Antitumor therapy (chemotherapy, antibody therapy, molecular targeted therapy,
                  retinoid therapy, hormonal therapy, or investigational agent) at least 21 days
                  prior to cycle 1 day 1 (C1D1) KRT-232 (AMG 232) + KRd

               -  Corticosteroids at least 3 weeks prior to starting KRT-232 (AMG 232) + KRd,
                  except for a dose equivalent to dexamethasone of =< 4 mg/day

               -  Autologous stem cell transplantation at least 12 weeks prior to starting KRT-232
                  (AMG 232) + KRd

               -  Allogeneic stem cell transplantation at least 24 weeks prior to starting KRT-232
                  (AMG 232) + KRd, and these subjects must also NOT have moderate to severe active
                  acute or chronic graft versus host disease (GVHD)

          -  Subjects must have Eastern Cooperative Oncology Group (ECOG) performance status =< 2
             (Karnofsky >= 60%)

          -  Absolute neutrophil count (ANC) >= 1,000/mcL without growth factors within 2 week of
             initiation of treatment

          -  Platelets >= 50,000 cells/mm^3 if marrow plasmacytosis < 50% OR platelet count >=
             30,000 cells/mm^3 if marrow plasmacytosis >= 50%

          -  Hemoglobin >= 8 g/dL within 2 weeks of the initiation of treatment

          -  Total bilirubin < 1.5 x institutional upper limit of normal (ULN) (< 2.0 x ULN for
             subjects with documented Gilbert's syndrome or < 3.0 x ULN for subjects for whom the
             indirect bilirubin level suggests an extrahepatic source of elevation)

          -  Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase
             [SGOT])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT])
             =< 2.5 x ULN

          -  Alkaline phosphatase < 2.0 x ULN (if liver or bone disease are present, < 3.0 x ULN)

          -  Creatinine clearance >= 50 mL/min/1.73 m^2

          -  Prothrombin time (PT) or partial thromboplastin time (PTT) < 1.5 x upper limit of
             normal (ULN), OR international normalized ratio (INR) < 1.5

          -  Subjects who have received radiation therapy targeting > 10% of the bone marrow space
             must have completed this at least 2 weeks prior to starting therapy with KRT-232 (AMG
             232) + KRd

          -  Subjects must be able and willing to provide bone marrow biopsies/aspirates and buccal
             swab as requested by the protocol

          -  Subjects must be willing to undergo myeloma genotyping for TP53 mutation, insertion,
             or deletion at screening

          -  Subjects must have an estimated life expectancy of at least 3 months

          -  The effects of KRT-232 (AMG 232) on the developing human fetus are unknown; for this
             reason and because lenalidomide is known to be teratogenic, women of child-bearing
             potential must commit to either abstaining continuously from heterosexual sexual
             intercourse or agree to use 2 forms of adequate contraception or continuously abstain
             from the time of informed consent for the duration of study participation through 5
             weeks (women) after receiving the last dose of KRT-232 (AMG 232), lenalidomide, or
             carfilzomib; should a woman become pregnant or suspect she is pregnant while she or
             her partner is participating in this study, she should inform her treating physician
             immediately; men treated or enrolled on this protocol must also agree to use adequate
             contraception prior to the study, for the duration of study participation, and 3
             months after completion of KRT-232 (AMG 232) administration; this includes one highly
             effective form of contraception (e.g. intrauterine device [IUD], hormonal [birth
             control pills, injections, hormonal patches, vaginal rings or implants] or partner's
             vasectomy) and one additional effective contraceptive method (e.g. male latex or
             synthetic condom, diaphragm, or cervical cap)

          -  Subjects must be able to swallow medication

          -  Ability to understand and the willingness to sign a written informed consent document

        Exclusion Criteria:

          -  Subjects with myeloma that is relapsed and/or refractory to KRd when used in
             combination defined as progression of disease while on therapy or within 60 days of
             completing therapy

          -  Subjects must show evidence of wild-type (WT) p53 status on somatic tissue specimens
             as assessed by deoxyribonucleic acid (DNA) sequencing; note that since patients with
             relapsed myeloma have a rapidly proliferating disease, patient can be enrolled and
             begin treatment prior to obtaining the results of this test; patients who are
             discovered to have a TP53 mutation will be removed from study after cycle one and can
             continue on carfilzomib, lenalidomide, and dexamethasone (KRd); all enrolled patients
             will be followed for toxicity

          -  Subjects who have not recovered from toxicities from prior anti-tumor therapy, defined
             as not having resolved to Common Terminology Criteria for Adverse Events (CTCAE)
             version 5.0 grade 0 or 1, or to levels dictated in the eligibility criteria with the
             exception of alopecia (grade 2 or 3 toxicities from prior antitumor therapy that are
             considered irreversible [defined as having been present and stable for > 6 months],
             such as grade 2 chemotherapy-induced peripheral neuropathy, may be allowed if they are
             not otherwise described in the exclusion criteria AND there is agreement to allow by
             both the investigator and sponsor)

          -  Subjects who are receiving any other investigational agents

          -  Subjects who have undergone major surgery within 28 days of study day 1;
             vertebroplasty and/or kyphoplasty, which must have been performed at least 1 week
             prior to starting KRT-232 (AMG 232) + KRd

          -  Subjects with known central nervous system involvement of myeloma should be excluded
             from this clinical trial because of their poor prognosis and because they often
             develop progressive neurologic dysfunction that would confound the evaluation of
             neurologic and other adverse events

          -  Subjects with history of allergic reactions attributed to compounds of similar
             chemical or biologic composition to KRT-232 (AMG 232) or carfilzomib, lenalidomide, or
             dexamethasone

          -  Subjects' medication list such as herbal medicines (e.g., St. John's wort), vitamins,
             and supplements will be reviewed before starting first dose of KRT-232 (AMG 232) and
             at each clinic visit; any potential drug interactions will be brought and discussed
             with the principal investigator; use of any known CYP3A4 substrates with narrow
             therapeutic window (such as alfentanil, astemizole, cisapride, dihydroergotamine,
             pimozide, quinidine, sirolimus, or terfanide) within the 14 days prior to receiving
             the first dose of KRT-232 (AMG 232) is not permitted; other medications (such as
             fentanyl and oxycodone) may be allowed per investigator's assessment/evaluation

          -  Treatment with medications known to cause QTc interval prolongation within 7 days of
             study day 1 is not permitted unless approved by the sponsor; use of ondansetron is
             permitted for treatment of nausea and vomiting

          -  Current use of warfarin, factor Xa inhibitors and direct thrombin inhibitors; Note:
             low molecular weight heparin and prophylactic low dose warfarin are permitted; PT/PTT
             must meet the inclusion criteria; subjects taking warfarin must have their INR
             followed closely

          -  Uncontrolled intercurrent illness including, but not limited to, ongoing or active
             infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac
             arrhythmia, or psychiatric illness/social situations that would limit compliance with
             study requirements

          -  Subjects with myocardial infarction within 6 months of study day 1, symptomatic
             congestive heart failure (New York Heart Association [NYHA] class III and higher),
             unstable angina, or cardiac arrhythmia requiring medication are excluded

          -  Subjects with gastrointestinal (GI) tract disease causing the inability to take oral
             medication, malabsorption syndrome, requirement for intravenous alimentation, prior
             surgical procedures affecting absorption, uncontrolled inflammatory GI disease (e.g.,
             Crohn's disease, ulcerative colitis)

          -  Subjects with history of bleeding diathesis

          -  Subjects with active infection requiring IV antibiotics within 2 weeks of study
             enrollment (day 1) are excluded

          -  Positive hepatitis B surface antigen (HepBsAg) (indicative of chronic hepatitis B),
             positive hepatitis total core antibody with negative HBsAG (suggestive of occult
             hepatitis B), or detectable hepatitis C virus RNA by a polymerase-chain reaction (PCR)
             assay (indicative of active hepatitis C - screening is generally done by hepatitis C
             antibody [HepCAb], followed by hepatitis C virus RNA by PCR if HepCAb is positive);
             subjects with hepatitis B virus suppressed on therapy, and previously
             treated/eradicated hepatitis C virus are eligible for study

          -  Human immunodeficiency virus (HIV)-positive subjects positive for human
             immunodeficiency virus (HIV) are NOT excluded from this study, but HIV-positive
             subjects must have:

               -  A stable regimen of highly active anti-retroviral therapy (HAART)

               -  No requirement for concurrent antibiotics or antifungal agents for the prevention
                  of opportunistic infections

               -  CD4 count above 250 cells/mcL and an undetectable HIV viral load on standard
                  PCR-based test

          -  Pregnant women are excluded from this study because KRT-232 (AMG 232) is an agent with
             the potential for teratogenic or abortifacient effects; because there is an unknown
             but potential risk for adverse events in nursing infants secondary to treatment of the
             mother with KRT-232 (AMG 232), breastfeeding should be discontinued if the mother is
             treated with KRT-232 (AMG 232); these potential risks may also apply to other agents
             used in this study

          -  Women who are lactating/breast feeding or who plan to breastfeed while on study
             through 1 week after receiving the last dose of study drug

          -  Subjects with prior treatment with an MDM2 inhibitor