We study the coupling of localized surface plasmon (LSP) and surface-plasmon polariton (SPP) modes in a system composed of a metallic nanoparticle chain separated from a thin metallic film by a dielectric spacer. The thickness of such a spacer influences the level of interaction between LSP and SPP modes and controls the electromagnetic enhancement in this system. An enhancement with narrow resonances can be observed for appropriate parameters. The high-resonance quality factor and tunability of this system make it a very promising candidate for biosensing and surface-enhanced spectroscopy applications. (C) 2009 Optical Society of America