Alice (Amy Huberman) lives with her boyfriend Mitch (Stephen Wight) and their gay best friend Richie (Emun Elliott).
Alice and Richie go into panic mode about their suitability as future parents, and so Mitch entrusts them with a robot baby from the antenatal class to practice on.
Ben is tall, handsome, rich, charming, successful and Alice's ex from four and a half years ago.
When plans backfire, Richie ends up leaving Alice and Mitch to spend the day with Dave, who unveils his own special birthday surprise.
But that means Richie leaving Alice and Mitch on the night they've planned so hard for so long to make special.
Mitch and Richie escape for the evening to a local bar, and run into Wendy; a ballsy, feisty, fabulous girl who reminds them very much of a pre-pregnancy Alice.
How long can they hold out before they're drawn back into Wendy's arms, and how will Alice react when the two women finally meet?
The threesome prepares for Alice's 'Final Push Party' with some questionable costume choices from the boys... Mitch decides it's time to get a career but first must re-sit his school exams.
Catriona Wightman, writing for Digital Spy, also praised the series, coming to the conclusion that "it's really rather good indeed.
The potentially quite unlikeable situation and characters have proved to be anything but, and some great set-piece lines and scenes really made us laugh out loud.
"[9] Writing for The Daily Telegraph, Catherine Gee said "Threesome throws up some funny moments and there's plenty of good chemistry between its stars.
"[8] Writing a negative review, again for The Guardian, Martin Skegg said "presumably it's meant to be funny, but you'll be searching high and low for the jokes.
"[8] David Crawford writing for the Radio Times gave a highly positive review, saying "starting from a preposterous premise, this rambunctious comedy manages to get hearty, and frequently filthy, laughs from its unlikely situation.
The humour is suitably broad for the subject matter, but there are neat gags, and wonderful physical comedy.
"[8] Liam Murphy, writing for On the Box, gave a mixed review, saying "this is a sitcom with potential and as long as it avoids the trappings of most comedy pregnancies (see season 8 of Friends) then I might just watch the rest of the series!