Define the quadratic family of order two as F µ (x, y) = (y, −x 2 + µx), where µ is a real parameter. The boundary of the basin of attraction of the fixed point at ∞ is an invariant curve for µ < 4, and is a Cantor set for µ > 4. Perturbations of F µ with µ = 4 were studied in Romero et al (2001 Discrete Continuous Dynam. Syst. 7 35) (also in higher dimension), where it was proved that these situations persist. Now we study perturbations of the bifurcation point µ = 4, where the explosion of the basin, B ∞ , occurs. We prove that either there exists a connected invariant curve J contained in the boundary of the basin, or the set of critical points is a subset of B ∞ and the boundary has uncountably many components accumulated by the pre-images of the analytic continuation of the fixed point at the origin. The curve J undergoes a fractalization process until it ceases to exist.