Blending consensus historical events and personages with imaginary occult forces is a strong recipe for counterfactual storytelling goodness that combines the best of two worlds: resonant history with wild-eyed fantasy. The formula has worked for Mike Mignola’s Hellboy franchise, as well as Charles Stross’s Laundry series. Ian Tregellis’s Milkweed Triptych is the latest such hybrid, zestily offering a suspenseful take on history rerouted by the uncanny.