diff --git a/cmd/marathon-resource/actions/actions.go b/cmd/marathon-resource/actions/actions.go
index 0dc356f..f412b9e 100644
--- a/cmd/marathon-resource/actions/actions.go
+++ b/cmd/marathon-resource/actions/actions.go
@@ -104,3 +104,15 @@ deployloop:
 	return IOOutput{Version: Version{Ref: did.Version}}, nil
 
 }
+
+// In shall
+func In(input InputJSON, apiclient marathon.Marathoner) (IOOutput, error) {
+
+	app, err := apiclient.GetApp(input.Source.AppID, input.Version.Ref)
+	if err != nil {
+		return IOOutput{}, err
+	}
+
+	return IOOutput{Version: Version{Ref: app.Version}}, nil
+
+}
diff --git a/cmd/marathon-resource/actions/actions_test.go b/cmd/marathon-resource/actions/actions_test.go
index e65277a..dd156f2 100644
--- a/cmd/marathon-resource/actions/actions_test.go
+++ b/cmd/marathon-resource/actions/actions_test.go
@@ -151,3 +151,62 @@ func TestOut(t *testing.T) {
 		}
 	}
 }
+
+func TestIn(t *testing.T) {
+	var (
+		ctrl           = gomock.NewController(t)
+		mockMarathoner = mocks.NewMockMarathoner(ctrl)
+	)
+	defer ctrl.Finish()
+
+	gomock.InOrder(
+		mockMarathoner.EXPECT().GetApp("bar", "foo").Times(1).Return(gomarathon.Application{Version: "foo"}, nil),
+		mockMarathoner.EXPECT().GetApp("baz", "quux").Times(1).Return(gomarathon.Application{}, errors.New("Bad stuff")),
+	)
+
+	type args struct {
+		input     InputJSON
+		apiclient marathon.Marathoner
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    IOOutput
+		wantErr bool
+	}{
+		{
+			"Works",
+			args{
+				input: InputJSON{
+					Source:  Source{AppID: "bar"},
+					Version: Version{Ref: "foo"},
+				},
+				apiclient: mockMarathoner,
+			},
+			IOOutput{Version: Version{Ref: "foo"}},
+			false,
+		},
+		{
+			"Errors",
+			args{
+				input: InputJSON{
+					Source:  Source{AppID: "baz"},
+					Version: Version{Ref: "quux"},
+				},
+				apiclient: mockMarathoner,
+			},
+			IOOutput{},
+			true,
+		},
+	}
+	for _, tt := range tests {
+		got, err := In(tt.args.input, tt.args.apiclient)
+		if (err != nil) != tt.wantErr {
+			t.Errorf("%q. In() error = %v, wantErr %v", tt.name, err, tt.wantErr)
+			continue
+		}
+		if !reflect.DeepEqual(got, tt.want) {
+			t.Errorf("%q. In() = %v, want %v", tt.name, got, tt.want)
+		}
+	}
+}
diff --git a/cmd/marathon-resource/main.go b/cmd/marathon-resource/main.go
index 66e617b..d39db60 100644
--- a/cmd/marathon-resource/main.go
+++ b/cmd/marathon-resource/main.go
@@ -44,8 +44,17 @@ func main() {
 	switch os.Args[1] {
 	case check:
 		//TODO: do check
+
 	case in:
-		//TODO: do in
+		output, err := actions.In(input, m)
+		if err != nil {
+			logger.WithError(err).Fatalf("Unable to get APP info from marathon: %s", err)
+		}
+		if err = encoder.Encode(output); err != nil {
+			logger.WithError(err).Fatalf("Failed to write output: %s", err)
+		}
+		return
+
 	case out:
 		output, err := actions.Out(input, os.Args[2], m)
 		if err != nil {