  We demonstrate a multiphoton Rydberg dark resonance where a Lambda-system is
coupled to a Rydberg state. This N-type level scheme combines the ability to
slow and store light pulses associated with long lived ground state
superpositions, with the strongly interacting character of Rydberg states. For
the nd_{5/2} Rydberg state in 87Rb (with n=26 or 44) and a beam size of 1 mm we
observe a resonance linewidth of less than 100 kHz in a room temperature atomic
ensemble limited by transit-time broadening. The resonance is switchable with
an electric field of order 1 V/cm. We show that, even when photons with
different wavevectors are involved, the resonance can be Doppler-free.
Applications in electro-optic switching and photonic phase gates are discussed.
