diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9482c7e..5c050d9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,9 +4,13 @@ All notable changes to this project will be documented in this file.
 
 ## [unreleased]
 
+### Features
+
+- Feat: Add support for invoke
+
 ### Miscellaneous Tasks
 
-- Chore: replace nix shell with flake
+- Chore: replace nix shell with flake (#81)
 
 ## [0.2.1] - 2024-05-15
 
diff --git a/flake.nix b/flake.nix
index 846e075..30a314e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -14,6 +14,7 @@
           nativeBuildInputs = with pkgs; [
             elixir
             erlang_27
+            nodejs_18 # need this to install inngest-cli for now
 
             # LSPs
             elixir-ls
diff --git a/lib/inngest/error.ex b/lib/inngest/error.ex
index f917cbe..eb9879f 100644
--- a/lib/inngest/error.ex
+++ b/lib/inngest/error.ex
@@ -1,3 +1,22 @@
+defmodule Inngest.Error do
+  @moduledoc """
+  A generic Inngest Error.
+  Used to format errors into a structure that can be parsed by the UI
+  """
+
+  defstruct [:error, stack: nil]
+end
+
+defimpl Jason.Encoder, for: Inngest.Error do
+  def encode(value, opts) do
+    error = Map.get(value, :error)
+    stacktrace = Exception.format(:error, error, Map.get(value, :stack))
+
+    %{name: error.__struct__, message: error.message, stack: stacktrace}
+    |> Jason.Encode.map(opts)
+  end
+end
+
 defmodule Inngest.NonRetriableError do
   @moduledoc """
   Error signaling to not retry
diff --git a/lib/inngest/response.ex b/lib/inngest/response.ex
index 9ad1c43..5ef320f 100644
--- a/lib/inngest/response.ex
+++ b/lib/inngest/response.ex
@@ -54,7 +54,8 @@ defmodule Inngest.SdkResponse do
     status = if retry, do: 500, else: 400
 
     encoded =
-      case Exception.format(:error, error, stacktrace) |> Jason.encode() do
+      case %Inngest.Error{error: error, stack: stacktrace}
+           |> Jason.encode() do
         {:ok, encoded} -> encoded
         {:error, _} -> "Failed to encode error: #{error}"
       end
diff --git a/lib/inngest/router/invoke.ex b/lib/inngest/router/invoke.ex
index 80df954..f7b0e2d 100644
--- a/lib/inngest/router/invoke.ex
+++ b/lib/inngest/router/invoke.ex
@@ -97,7 +97,7 @@ defmodule Inngest.Router.Invoke do
       retry in Inngest.RetryAfterError ->
         delay = Map.get(retry, :seconds)
 
-        SdkResponse.from_result({:error, retry.message},
+        SdkResponse.from_result({:error, retry},
           retry: delay,
           stacktrace: __STACKTRACE__
         )
diff --git a/lib/inngest/step_tool.ex b/lib/inngest/step_tool.ex
index b17be20..4460af5 100644
--- a/lib/inngest/step_tool.ex
+++ b/lib/inngest/step_tool.ex
@@ -117,6 +117,55 @@ defmodule Inngest.StepTool do
     end
   end
 
+  @spec invoke(Context.t(), binary(), map()) :: map()
+  def invoke(%{steps: steps} = ctx, step_id, opts) do
+    op = UnhashedOp.new(ctx, "InvokeFunction", step_id, opts)
+    hashed_id = UnhashedOp.hash(op)
+
+    case Map.get(steps, hashed_id) do
+      nil ->
+        func = Map.get(opts, :function)
+        data = Map.get(opts, :data)
+        timeout = Map.get(opts, :timeout)
+        v = Map.get(opts, :v)
+
+        generator_otps =
+          if Map.has_key?(opts, :timeout) do
+            %{
+              function_id: func.slug(),
+              payload: %{data: data, v: v},
+              timeout: timeout
+            }
+          else
+            %{
+              function_id: func.slug(),
+              payload: %{data: data, v: v}
+            }
+          end
+
+        throw(%GeneratorOpCode{
+          id: hashed_id,
+          name: step_id,
+          display_name: step_id,
+          op: op.op,
+          opts: generator_otps
+        })
+
+      %{
+        "error" => %{
+          "name" => "InngestInvokeTimeoutError",
+          "error" => message,
+          "message" => _
+        }
+      } ->
+        raise Inngest.NonRetriableError, message: message
+
+      # return value if found
+      val ->
+        val
+    end
+  end
+
   def send_event(%{steps: steps} = ctx, step_id, events) do
     op = UnhashedOp.new(ctx, "Step", step_id)
     hashed_id = UnhashedOp.hash(op)
diff --git a/test/inngest/function/cases/failure_handler_test.exs b/test/inngest/function/cases/failure_handler_test.exs
index 0b1b6b5..1ff476b 100644
--- a/test/inngest/function/cases/failure_handler_test.exs
+++ b/test/inngest/function/cases/failure_handler_test.exs
@@ -17,13 +17,17 @@ defmodule Inngest.Function.Cases.RetriableTest do
               "data" => [
                 %{
                   "run_id" => _run_id,
-                  "output" => stacktrace,
+                  "output" => %{
+                    "message" => message,
+                    "name" => "Elixir.Inngest.RetryAfterError",
+                    "stack" => _
+                  },
                   "status" => "Failed"
                 }
               ]
             }} = DevServer.run_ids(event_id)
 
-    assert stacktrace =~ "YOLO!!!"
+    assert message == "YOLO!!!"
 
     {:ok, %{"data" => events}} = DevServer.list_events()
 
diff --git a/test/inngest/function/cases/invoke_test.exs b/test/inngest/function/cases/invoke_test.exs
new file mode 100644
index 0000000..3ba4622
--- /dev/null
+++ b/test/inngest/function/cases/invoke_test.exs
@@ -0,0 +1,25 @@
+defmodule Inngest.Function.Cases.InvokeTest do
+  use ExUnit.Case, async: true
+
+  alias Inngest.Test.DevServer
+  import Inngest.Test.Helper
+
+  @default_sleep 5_000
+
+  @tag :integration
+  test "should run successfully" do
+    event_id = send_test_event("test/invoke.caller")
+    Process.sleep(@default_sleep)
+
+    assert {:ok,
+            %{
+              "data" => [
+                %{
+                  "output" => %{"data" => "INVOKED!"},
+                  "run_id" => _,
+                  "status" => "Completed"
+                }
+              ]
+            }} = DevServer.run_ids(event_id)
+  end
+end
diff --git a/test/inngest/function/cases/invoke_timeout_test.exs b/test/inngest/function/cases/invoke_timeout_test.exs
new file mode 100644
index 0000000..39d6cbf
--- /dev/null
+++ b/test/inngest/function/cases/invoke_timeout_test.exs
@@ -0,0 +1,36 @@
+defmodule Inngest.Function.Cases.InvokeTimeoutTest do
+  use ExUnit.Case, async: true
+
+  alias Inngest.Test.DevServer
+  import Inngest.Test.Helper
+
+  @default_sleep 5_000
+
+  @tag :integration
+  test "should fail with timeout error" do
+    event_id = send_test_event("test/invoke.timeout.caller")
+    Process.sleep(@default_sleep)
+
+    assert {
+             :ok,
+             %{
+               "data" => [
+                 %{
+                   "output" => %{
+                     "name" => error,
+                     "message" => message,
+                     "stack" => _
+                   },
+                   "run_id" => _,
+                   "status" => "Failed"
+                 }
+               ]
+             }
+           } = DevServer.run_ids(event_id)
+
+    assert error == "Elixir.Inngest.NonRetriableError"
+
+    assert message ==
+             "InngestInvokeTimeoutError: Timed out waiting for invoked function to complete"
+  end
+end
diff --git a/test/inngest/function/cases/no_retry_test.exs b/test/inngest/function/cases/no_retry_test.exs
index 4cd8372..2441f73 100644
--- a/test/inngest/function/cases/no_retry_test.exs
+++ b/test/inngest/function/cases/no_retry_test.exs
@@ -15,13 +15,17 @@ defmodule Inngest.Function.Cases.NoRetryTest do
             %{
               "data" => [
                 %{
-                  "output" => stacktrace,
+                  "output" => %{
+                    "message" => message,
+                    "name" => "Elixir.Inngest.NonRetriableError",
+                    "stack" => _
+                  },
                   "run_id" => _run_id,
                   "status" => "Failed"
                 }
               ]
             }} = DevServer.run_ids(event_id)
 
-    assert stacktrace =~ "not retrying!"
+    assert message == "not retrying!"
   end
 end
diff --git a/test/support/cases/invoke_fn.ex b/test/support/cases/invoke_fn.ex
new file mode 100644
index 0000000..bb496e4
--- /dev/null
+++ b/test/support/cases/invoke_fn.ex
@@ -0,0 +1,38 @@
+defmodule Inngest.Test.Case.InvokeCallerFn do
+  @moduledoc false
+
+  use Inngest.Function
+
+  @func %FnOpts{id: "invoke-caller", name: "Invoke Caller"}
+  @trigger %Trigger{event: "test/invoke.caller"}
+
+  @impl true
+  def exec(ctx, %{step: step} = _args) do
+    _ = step.run(ctx, "step-1", fn -> %{hello: "world"} end)
+
+    res =
+      step.invoke(ctx, "caller", %{
+        function: Inngest.Test.Case.InvokedFn,
+        data: %{yolo: true},
+        timeout: "10s"
+      })
+
+    {:ok, res}
+  end
+end
+
+defmodule Inngest.Test.Case.InvokedFn do
+  @moduledoc false
+
+  use Inngest.Function
+
+  @func %FnOpts{id: "invoke-target", name: "Invoked"}
+  @trigger %Trigger{event: "test/invoked"}
+
+  @impl true
+  def exec(ctx, %{step: step} = _args) do
+    _ = step.run(ctx, "invoked", fn -> "YO!" end)
+
+    {:ok, "INVOKED!"}
+  end
+end
diff --git a/test/support/cases/invoke_timeout_fn.ex b/test/support/cases/invoke_timeout_fn.ex
new file mode 100644
index 0000000..7bd02c7
--- /dev/null
+++ b/test/support/cases/invoke_timeout_fn.ex
@@ -0,0 +1,39 @@
+defmodule Inngest.Test.Case.InvokeTimeoutCallerFn do
+  @moduledoc false
+
+  use Inngest.Function
+
+  @func %FnOpts{id: "invoke-timeout-caller", name: "Invoke Timeout Caller"}
+  @trigger %Trigger{event: "test/invoke.timeout.caller"}
+
+  @impl true
+  def exec(ctx, %{step: step} = _args) do
+    _ = step.run(ctx, "step-1", fn -> %{hello: "world"} end)
+
+    _ =
+      step.invoke(ctx, "caller", %{
+        function: Inngest.Test.Case.InvokedLongFn,
+        data: %{yolo: true},
+        timeout: "1s"
+      })
+
+    {:ok, "TIMED OUT"}
+  end
+end
+
+defmodule Inngest.Test.Case.InvokedLongFn do
+  @moduledoc false
+
+  use Inngest.Function
+
+  @func %FnOpts{id: "invoke-long-target", name: "Invoked Long"}
+  @trigger %Trigger{event: "test/invoked.long"}
+
+  @impl true
+  def exec(ctx, %{step: step} = _args) do
+    _ = step.sleep(ctx, "sleep", "5s")
+    _ = step.run(ctx, "invoked", fn -> "YO!" end)
+
+    {:ok, "INVOKED!"}
+  end
+end