We study the moduli space of pairs (X, H) consisting of a cubic threefold X and a hyperplane H in P 4 . The interest in this moduli comes from two sources: the study of certain weighted hypersurfaces whose middle cohomology admit Hodge structures of K3 type and, on the other hand, the study of the singularity O 16 (the cone over a cubic surface). In this paper, we give a Hodge theoretic construction of the moduli space of cubic pairs by relating (X, H) to certain "lattice polarized" cubic fourfolds Y . A period map for the pairs (X, H) is then defined using the periods of the cubic fourfolds Y . The main result is that the period map induces an isomorphism between a GIT model for the pairs (X, H) and the Baily-Borel compactification of some locally symmetric domain of type IV.but also admits an automorphism of order 3; the corresponding Mumford-Tate subdomain is a 7-dimensional ball.Remark 0.5. We point out that after the appearance of our manuscript, Chenglong Yu and Zhiwei Zheng [YZ18] have made a systematic study of the moduli space of symmetric cubic fourfolds (i.e. cubics with specified automorphism group). Since cubics with Eckardt points can be characterized as cubics admitting an involution that fixes a hyperplane, they fit into the loc. cit. framework. While some overlap between our results and those of Yu-Zheng exist (see esp. [YZ18, Prop. 6.5]), the focus of the two papers is essentially complementary.