With its story of a mother and son consumed in different ways by a dreadful loss, Jennifer Kent’s focused debut feature excels at what you might call grief horror. The Babadook picks up seven years after Amelia (Essie Davis) loses her husband to a car accident on the way to the hospital to give birth to her son Samuel (Noah Wiseman). Amelia has trouble putting on a good face with her friends and at her job as a nurse at a home for the elderly, especially once Samuel begins to speak of defending her from some horrible bogeyman. The Babadook of the title turns out to be a character in a children’s book that appears on Samuel’s bedtime-reading bookshelf, before assuming a physical presence. But even before that happens, the two actors and the house itself make a grim impression, albeit with traces of dark humor. Davis’s performance gets across a visceral sense of the experience of grief, terribly distant and yet tenderly sensitive to stress, finally erupting into rage against her son. The precocious Wiseman finds fresh nuances in the irrepressible character of Samuel, an oddball who’s concerned for but also wary of his mother in her confused state. But equally vital are cinematographer Radek Ladzcuk’s sculpted, shadowy interiors, as well as Kent’s enveloping sense of mood and attention to detail. And the unexpected ending finds a rare emotional realism in what could have been a run-of-the-mill creepshow.