Worried Eileen's sister Julie Carp will spy on the fireman in a bid to catch him out, according to the Daily Star.
Factory worker Julie will don a scarf, glasses and a pair of binoculars as she secretly tracks Paul for a day.
A Corrie source teased: "Eileen thinks he's up to something so Julie offers her services - Miss Marple eat your heart out!"
Eileen and Paul started dating in 2010 when he came to rescue her after she had trapped her head in some railings.
However, their relationship was tested upon the discovery of Paul's wife Lesley, who had been diagnosed with Alzheimer's and ended up staying at 11 Coronation Street.
Coronation Street continues tonight at 7.30pm on ITV.
New! Digital Spy Soap Scoop video - watch Amie Parker-Williams discuss the biggest storylines on the way in Coronation Street, EastEnders, Emmerdale and Hollyoaks: